Heat pumps, repaired and serviced by an engineer who understands how they actually work.
Heat pump work is the part of this job I care most about — finding the fault on a system nobody else can sort, working out why it’s misbehaving, and putting it right. I install them too, but for me installation is how I build long-term clients: the work I love is keeping their systems running properly for the fifteen years afterwards. I’m one engineer — the person who quotes the work is the person who turns up and does it. F-Gas registered, factory-trained on the major brands, and far more interested in fixing kit than selling you a new system.
Why your heat pump might not be working as promised
A high proportion of the heat pump enquiries I get come from homeowners whose system was installed by someone else and isn’t performing the way they were sold on. The patterns are the same again and again.
“We haven’t had a proper hot shower since the heat pump was fitted.”
The unit can’t satisfy the hot water demand and the heating demand at the same time. It alternates between the two and falls short on both. The root cause is almost always incorrect sizing. If the unit is undersized for the property, it cycles between heating and hot water trying to keep up, goes into defrost cycles more often than it should, can’t deliver enough capacity to either circuit, and falls back on the immersion heater to make up the shortfall. If the unit is oversized, you’d think more capacity solves the problem — but modern inverter-driven heat pumps can only modulate down to around 30% of their rated output. Below that they cycle on and off. Most units are protected by a limit on the number of start/stop cycles per hour, so they fire up briefly, hit the cycle limit, sit idle until it resets, fire up again, and so on. Neither the heating nor the hot water gets satisfied properly. The answer in both cases is correct sizing from the start — neither too small nor too big — and where the demand profile justifies it, sometimes two smaller units in cascade work better than one larger one. More on that in the install section below.
“Our energy bills are three to four times what we were told they’d be.”
Almost always a combination of: incorrect sizing (either undersized so the unit can’t meet demand, or oversized so it cycles inefficiently), an immersion heater quietly compensating for what the heat pump can’t deliver, no insulation work done before the install, and a controller set up by someone who didn’t understand the system.
“The unit keeps icing up in winter.”
First, some context: all air source heat pumps ice up to some extent in winter. They work by moving heat from the outdoor air into your house — and when the outdoor air is cold and humid, moisture in that air condenses on the cold evaporator coils and freezes. This is normal and expected. Heat pumps have built-in defrost cycles to handle it: the controller decides when to defrost based on a combination of air temperature, evaporator-bottom temperature, suction pressure and compressor run time. When the algorithm decides it’s time, the unit briefly reverses to send warm refrigerant through the outdoor coil and melt the ice. That’s by design.
What’s not normal is icing up so badly that the unit can’t recover. That points to a real fault or a real install problem. Common causes I see: the condensate drain from the outdoor unit was never connected, so meltwater pools at the base, freezes solid, and every subsequent defrost dumps more water onto the growing block of ice — a frozen drain quickly turns into a frozen unit. Less common but real: the evaporator coil sensor has failed, the controller never registers that the coil is iced up, and no defrost cycle is initiated. I’ve had clients pouring kettles of hot water over the outdoor unit every hour to keep it running until I could get there. Excessive defrost frequency can also point to undersizing, controller settings that are wrong for the climate, or refrigerant charge issues — all of which need a proper diagnostic to sort.
“The immersion heater is always on.”
It shouldn’t be. On a properly-set-up heat pump it runs occasionally for legionella pasteurisation cycles and as a fallback when outdoor temperatures crash. I’ve seen installs where the immersion was wired in from a fuse spur instead of through the heat pump controller, meaning it just runs continuously until the limescale build-up trips it.
“The installer told us not to touch anything.”
Probably because they wouldn’t be able to fix it again if you did. A heat pump is a major piece of equipment in your home — you should understand how to set hot water schedules, change setpoints, and see what mode it’s running in. If the installer left without teaching you, that’s on them.
“The radiators don’t get hot enough.”
This one has two completely different versions, and the first thing I do is work out which one I’m dealing with.
Version one — the house is actually cold. The radiators are running at 45–55°C (the normal flow temperature for a heat pump) but the rooms aren’t reaching comfort temperature. This is genuinely a problem and almost always points to undersized radiators. Existing radiators were sized for a gas boiler running at 75–80°C; at heat pump flow temperatures they put out roughly half their rated heat. The fix is upsizing radiators in the rooms that matter, sometimes adding fan coils (units that blow air across a finned exchanger and can deliver high heat output at low water temperatures), and addressing insulation. When the radiator survey gets skipped at install time and the heat pump is simply connected to the existing system, cold houses are the result.
Version two — the house is warm but the rads don’t feel hot to the touch, and the homeowner has been told this means something’s wrong. I’ve had clients tell me their radiators “aren’t hot enough” while the room temperature is sitting at 21°C and they’re perfectly comfortable. Years of gas boilers running radiators at 70°C+ condition people to expect that “warm room” means “scalding-hot radiator”. With a heat pump, if your radiators are at 45°C and the room is at comfort temperature, that’s a win: your bills are lower because the heat pump is running at a higher COP, and the room is warm. The radiator is supposed to warm the room, not your hand. The survey engineer should have explained this from the start — and when they don’t, I end up doing it on the first service visit.
When I get called to these systems, the first job is to diagnose what’s wrong. The second is to tell the homeowner plainly what it’ll cost to put right — and sometimes the answer is that the install was so far off the mark that the best route is to start over. Most of the time it’s recoverable: the right controller settings, a sensor replaced, the immersion rewired through the controller, a couple of larger radiators in the rooms that matter, a buffer tank fitted, a proper commissioning. Bills come down, comfort goes up, and the system starts behaving the way the brochure promised.
Repair and service any make. Install air source.
Heat pumps share more in common than they differ. The thermodynamics is the same, the controller logic is broadly the same, and an engineer who understands one well can diagnose most others competently. I’m factory-trained on the biggest brands and work confidently on the rest because the underlying engineering is shared.
How I approach an install differently
I’m not a high-volume installer and I’m not interested in becoming one. High-volume installers run on a different model — sales team, fixed-price packages, an engineer who fits the box and leaves. The economics push them to specify tight and lean on the customer’s immersion heater as the safety net when the unit can’t keep up. Being small, I can afford to spend the time getting it right at the design stage. A typical install with me goes like this.
Heat loss calculation (paid service)
Before I quote anything, I do a proper room-by-room heat loss calculation to the standards in the CIBSE Domestic Heating Design Guide (latest revision January 2026 — what heating engineers treat as the bible of the trade), using existing drawings or measuring the property in person. I work out the heat demand for each room, the total for the property, and the hot water demand from the household’s actual usage. It’s paid work because it takes hours and it’s the foundation every later number rests on — and you keep the results whether you go ahead with me or not. Without it, every subsequent figure is a guess.
System design
From the heat loss calc I size the heat pump, the cylinder, any radiator upgrades, the pipework and the buffer tank where needed — to match what your property actually needs, not what’s on the supplier’s promotion that month. Manufacturers offer heat pumps in fixed steps (for example 4, 6, 10, 12, 14, 18 kW), so the correct unit is the next size up from your calculated peak demand at design outdoor temperature. Slightly above is right; well above is wrong (it cycles and runs inefficiently); below is wrong (it struggles and the immersion quietly runs more than it should). For some properties the best answer isn’t one unit — it’s two smaller ones in cascade: one dedicated to heating while the other handles heating-plus-hot-water, so there’s always a unit free for each duty. That fixes the “no hot water when the heating’s on” problem while letting both units modulate at lower loads, keeping the COP high and the bills low. The bigger up-front cost is often paid back in lower running costs over the system’s life, and I’ll walk you through the numbers so you can decide.
Quote
Detailed and itemised, no surprises — the unit, the cylinder, any radiator changes, the pipework, the controls, the installation labour, the commissioning and the post-install support.
Install and commission
Done properly. The controller is set up for your actual property and your actual hot water habits. The immersion is wired correctly through the heat pump controller, not as a parallel circuit. The condensate drain is connected and run somewhere it won’t freeze. The system is balanced and tested under real operating conditions.
Handover
I sit down with you and explain how the system works, how to change settings, what the controller’s telling you, what to look out for and when to call. You leave that conversation understanding your own heating system.
Service and ongoing support
Annual service, fault diagnosis when needed, and a relationship that doesn’t end when the van pulls away.
The MCS and the £7,500 Boiler Upgrade Scheme grant — the plain version
MCS (Microgeneration Certification Scheme) accreditation is what unlocks the government’s Boiler Upgrade Scheme (BUS) grant, currently £7,500 toward a heat pump installation. To install MCS-accredited, an installer has to be MCS-registered as a business — an expensive ongoing accreditation most small engineers can’t justify. The alternative, and what I do, is to work through an “umbrella” scheme: an MCS-registered company sub-commissions my work and signs off the install under their MCS registration. That’s how a small, properly qualified engineer can offer MCS-accredited installs without holding the accreditation directly.
The catch: the umbrella charges for that service. As of mid-2026, the umbrella partners I’ve worked with charge somewhere between £1,400 and £2,200 plus VAT per install for their part — the heat loss verification, the design sign-off, the MCS certificate issuance. Different umbrellas charge different fees and change them periodically. That cost gets passed on to you, whether it’s itemised or rolled into the total. So the maths for the homeowner is:
- With MCS umbrella: the install qualifies for the £7,500 BUS grant. The umbrella adds £1,400–£2,200 + VAT to the cost. Net benefit: still substantial, but not the full £7,500.
- Without MCS: the install costs less because there’s no umbrella fee, but there’s no grant. The net cost can be higher or lower than the MCS route depending on system size and the umbrella fee at the time.
I offer both routes and quote both, so you can decide. I’ve no financial interest in pushing you one way or the other.
A word on the BUS grant itself
The £7,500 BUS grant is government money meant to encourage households off gas heating and to improve the home’s energy efficiency. The scheme documents are clear about the intent — it’s not just to subsidise a heat pump in isolation, it’s to support a transition that includes improving the property’s insulation so running costs are actually lower afterwards. In practice, plenty of installs happen with the grant claimed and no insulation work done, the heat pump struggling in an uninsulated property, the homeowner facing bills higher than they expected, and the grant money having mostly served to enrich the umbrella scheme rather than reduce the household’s costs. I’d rather help you spend the grant in the way the scheme was designed for: a properly-sized heat pump in a properly-prepared property, where the long-term running costs make the move worth it.
Why a poorly-designed install can cost more to run than the gas boiler it replaced
As of mid-2026 (Ofgem energy price cap, second quarter), the unit price of gas in the UK is around 5.74p per kWh and electricity is around 24.67p per kWh. Electricity is roughly 4.3 times more expensive per kWh than gas.
Heat pumps run on electricity; gas boilers burn gas. For a heat pump to deliver heat at the same running cost as the boiler it replaced, it has to produce more than 4.3 kWh of heat for every 1 kWh of electricity it draws. That ratio — heat out divided by electricity in — is the Coefficient of Performance, or COP. A COP of 4.3 breaks even against a gas boiler. Above 4.3 saves money. Below 4.3 costs more to run than the boiler it replaced.
Manufacturer brochures quote COP figures of 4.0, 4.5, sometimes higher. Those are measured under laboratory conditions, typically at mild outdoor temperatures and the lowest practical flow temperature. Real-world COPs in UK winter conditions, on systems that weren’t designed perfectly, are commonly 2.5–3.5 — below the 4.3 breakeven, which means running costs higher than the previous gas boiler.
That isn’t a reason not to fit a heat pump. It’s a reason to be clear about the conditions that make one worth fitting:
- The property needs to be properly insulated. Heat that leaks out has to be replaced. A heat pump in a leaky house runs long hours at high modulation, the COP drops and the bills climb. Insulation reduces the demand, the unit runs less hard, the COP stays high and the bills stay reasonable.
- The system needs to be designed for low flow temperatures. Heat pumps work best at 35–45°C. Radiators and pipework need to be sized for that. Underfloor heating is ideal. Existing radiators sized for an old 75°C system need upsizing, or replacing with fan coils in critical rooms.
- The system needs commissioning by someone who knows what they’re doing. Default controller settings are rarely right for any specific property. Weather compensation curves, schedule profiles, hot water priorities, the role of the immersion as backup — all of it needs setting up properly and reviewing periodically.
Most properties in Luton — certainly the older terraces and semis — need some insulation work before a heat pump makes financial sense. I always explain this before quoting. If the answer is “we don’t want the insulation work, we just want the heat pump”, I’ll still quote, but I’ll tell you plainly what the likely running costs will be.
Heat pumps don’t make heat. They move it. The job is to stop the heat leaking out in the first place.
How efficiently a heat pump moves heat depends on how cold it is outside and how big the unit is relative to your demand. You only need to heat the house at all because heat is leaking out through the walls, windows, roof, floor and air changes. Slow the leaks down and you have to replace less heat. Insulation, draughtproofing, better windows and properly-managed ventilation aren’t unrelated upgrades — they’re the foundation a heat pump install rests on. Without that foundation, the heat pump does more work than it should and you pay for it every month.
How the heat pump industry works — and where I differ
I have a difficult relationship with how the heat pump industry currently operates in the UK, and rather than gloss over it I’ll explain it.
The factory training courses for heat pumps are typically one day long, trying to compress an enormous amount into that time. The format assumes a grounding in refrigeration thermodynamics and F-Gas that not everyone in the room arrives with, and a single day can’t build it. Someone can leave with a certificate and a half-formed picture of how the system actually behaves. The unit gets installed, an umbrella scheme’s commissioning engineer comes in afterwards, sets the dip switches to a brochure spec, takes some measurements, fills in the boxes and leaves — and the client is told not to touch any settings or face a callout charge.
I’ve raised these points on multiple factory courses (Vaillant, Daikin, Mitsubishi, Worcester Bosch, Ideal, Intergas — heat pump and boiler training alike) over the years. The schemes are structured around shipping volume, not around quality of install.
I also have direct experience of disagreeing with an MCS umbrella partner over correct design. On one job I specified the unit and cylinder size I knew to be right for the client’s actual heat demand. The umbrella’s engineer refused to sign off the design because the unit wasn’t one they had a standard commissioning procedure for, and pushed the client toward a smaller unit they could commission against their generic template. The result: the client ended up using the immersion heater to compensate for the heat pump’s inability to deliver the required output. The system worked, technically. The bills are higher than they should be. Nobody in the chain except me saw a problem.
I won’t name the umbrella partner — the industry talks and I’d like to keep my options open — but I’ll say plainly: heat pump installs in the UK are too often driven by money and process rather than by standards or pride in the work. The good engineers are out there. The way to find one is to ask hard technical questions and see whether the answers come back specific and confident or generic and evasive.
Repair, service, install and design consultancy
Any make, anywhere
Diagnostic call-out at an hourly rate. Vaillant, Daikin, Mitsubishi Electric, Viessmann, Ideal, Grant, Samsung, LG, Midea, Ochsner and others. Cascades and single units, air source and ground source.
Annual service, any make
Refrigerant system check (F-Gas certified), controller review and reconfiguration where needed, sensor checks, defrost-cycle verification, condensate drainage check, immersion wiring and operation, hot water system check, system pressures, performance checked against design figures. Written service record issued.
Air-source, properly sized
Heat loss calculation as a paid first stage, then a properly-sized unit, cylinder and emitters. MCS-accredited (via umbrella) and non-MCS routes both available, with the cost difference clearly explained. Full commissioning and a proper handover.
Design consultancy, no commitment
Early-stage and want a heat loss calculation, a system sizing exercise and a straight assessment of whether your property is ready? I’ll do that as a standalone paid service. You’re not committed to using me for the install — the work is yours to take to whoever you like. See also my M&E design page.
How I price heat pump work
Heat loss calculation and design consultancy: a flat fee for typical domestic properties, quoted up front based on size and complexity. For larger or more complex jobs I agree the scope and cost before starting.
Repair and diagnostic call-out: an hourly rate, agreed before I arrive. I tell you what the diagnosis is and what it’ll cost to fix before doing the work.
Service: charged at an hourly rate. Most domestic heat pump services take 1.5 to 2.5 hours depending on the system. There’s a running joke among heat pump engineers fresh out of training — “the most important part of servicing a heat pump is showing up; the rest is mostly dusting off the outdoor unit”. It captures something real about how the industry treats servicing, and I don’t agree with it. A proper service genuinely takes time, because the operating sequence of a heat pump takes time: the compressor has a ramp-up sequence, the fans take time to stabilise, water in the system heats gradually, sensor readings update on slow cycles, settings changes have to be made and then waited out to test, the outdoor unit and indoor controller and hot water cylinder are in three different locations, and the cylinder itself needs servicing as a G3 unvented appliance separately from the heat pump. A heat pump service done in 30 minutes is a heat pump service that wasn’t done. Mine typically takes between 90 minutes and two and a half hours, and I issue a proper written service record.
Install: a detailed quote based on the heat loss calculation and system design. MCS and non-MCS routes both quoted so you can see the difference.
Parts: charged at a fair mark-up over my cost. The mark-up funds van stock (so most repairs can be done same-visit) and covers the 12-month parts-and-labour warranty on parts I supply.
Where I work
Luton and the surrounding area for routine work — Dunstable, Harpenden, St Albans, Leighton Buzzard, Hitchin, Hemel Hempstead, Central Bedfordshire, Hertfordshire and Buckinghamshire. For heat pump work specifically I travel further on request — across London, Essex, north Kent, and into Surrey where the job justifies the trip. Travel is charged at cost and quoted up front; I’d rather tell you the real figure than bury it in the quote.
Qualifications and cover
- F-Gas certified: FGAS2002910 — legally required for any heat pump refrigerant work
- Gas Safe registered: 577195 (domestic, up to 70 kW) — relevant for the heating-system tie-in
- WaterSafe registered through CIPHE: 00047447
- IGEM Licensed Gas Technician: 175195
- G3 unvented hot water systems
- 18th Edition BS 7671, plus Level 3 electrical awards
- £5 million public liability cover
- 24-month workmanship warranty, plus a 12-month parts-and-labour warranty on parts I supply
- Manufacturer extended warranties — typically 5–7 years on heat pumps installed under accredited installer schemes
Factory trained on Vaillant, Daikin, Mitsubishi Electric, Mitsubishi Heavy Industries, Viessmann, Ideal and Grant (air source and ground source).
Talk to the engineer.
If your heat pump isn’t behaving the way you were told it would, if the bills are higher than you expected, if the hot water never seems quite right, or if you’re thinking about installing one and want a straight conversation before you commit — call. Phone advice is free, and often I can tell you what’s going on without a visit. If you need an engineer, I’ll book you in, and I’ll be the engineer who turns up.
Call 07864 757929
Email office@bson247.co.uk
Building Services ON 247 — Luton. Heat pumps repaired, serviced and installed by the engineer who does the work. Monday to Saturday, 7am–7pm.
Heat pump repair in Luton — your questions answered
The things people most often ask me about heat pumps before booking. If yours isn’t here, just call and ask — phone advice is free.
How much does heat pump repair cost?
Repair and diagnosis is £90 an hour in Luton, or £150 an hour outside it, agreed before I set off, with no separate call-out fee. I tell you what the fault is and what the fix will cost before I do the work, and parts are charged separately at a fair mark-up.
A full service usually takes 1.5 to 2.5 hours done properly — it’s a real job with the compressor and fans needing time to settle, not just dusting off the outdoor unit.
Can you repair any make of heat pump?
Yes. A lot of installers will only touch the brand they fit, which leaves people stuck when their original installer moves on or stops trading.
I’m F-Gas registered and factory-trained across six heat-pump brands, and I’ll diagnose and repair any make — finding the fault on a system nobody else can sort is the part of this work I enjoy most.
Can I get the £7,500 Boiler Upgrade Scheme grant through you?
Yes, through an MCS umbrella scheme. The grant needs the installation signed off by an MCS-registered company. Holding that accreditation directly is an expensive ongoing cost most one-person engineers can’t justify, so I work with an MCS-registered umbrella partner who verifies the design and issues the certificate.
They charge for that — roughly £1,400 to £2,200 plus VAT per install as of mid-2026 — and I pass that cost on to you openly rather than burying it in the quote.
Will a heat pump actually cost less to run than my gas boiler?
Only if it’s designed and sized properly for your home — and that’s the whole game. With a proper room-by-room heat-loss calculation, radiators sized for lower flow temperatures and the system set up right, a heat pump can run cheaper than a gas boiler.
Fitted without that groundwork, it can genuinely cost more to run than the boiler it replaced. I’ll tell you straight which outcome your property is heading for before you commit a penny.
My heat pump isn’t heating the house, or the bills are huge — why?
Usually it’s a design or set-up problem rather than a broken unit. The most common causes I find are a heat pump undersized for the property, a flow temperature set too high, weather compensation or controls set up wrongly, or radiators too small to give out heat at the lower temperatures a heat pump runs at.
I work out the real cause rather than just topping up refrigerant and hoping it holds.
Do I need a heat loss calculation, and why does it cost?
Yes — it’s the foundation every other figure rests on. I work out the heat demand room by room to the CIBSE Domestic Heating Design Guide, either from your drawings or by measuring the property in person.
It’s paid work because it takes hours, and you keep the results whether you go ahead with me or not. Skip it, and every number that follows — the size of the unit, the radiators, the running cost — is just a guess.
What heat pump brands do you work on and install?
I’m factory-trained across six heat-pump brands, including Daikin and Mitsubishi — both Mitsubishi Electric and Mitsubishi Heavy Industries.
I install air-source heat pumps, and I’ll repair and service any make, not only the ones I fit.
How often should a heat pump be serviced, and how long do they last?
Once a year, and done properly that takes 1.5 to 2.5 hours — the compressor and fans need time to settle, readings update on slow cycles, and the hot water cylinder needs its own G3 service on top.
Looked after that way, a well-designed system will run fifteen to twenty years. I service any make, not just installs I’ve done myself.
Which areas do you cover for heat pump work?
Luton and the surrounding towns — Dunstable, Harpenden, St Albans, Leighton Buzzard, Hitchin and Hemel Hempstead — for routine work.
For heat pumps specifically I’ll travel further when the job justifies it: across London, Essex, north Kent and into Surrey. Travel is charged at cost and quoted up front, never buried in the price.
Got a heat pump that isn’t behaving, or weighing one up? Call me on 07864 757929 — I’ll give you a straight answer.