Vaillant boilers, repaired, serviced and installed by an Advance Installer.

Premium engineering, built to outlast the warranty

Vaillant has been making heating products since 1874, founded by Johann Vaillant in Remscheid, Germany, where it’s still headquartered. The boilers I install in UK homes are built at Vaillant’s Belper facility in Derbyshire — Vaillant was the first manufacturer to produce both gas boilers and air source heat pumps on UK soil, with the heat pump line at Belper opening in recent years.

The brand sits at the premium end of the UK market alongside Viessmann and Worcester Bosch. The ecoTEC range — first launched here in the early 2000s — set the benchmark for stainless steel heat exchangers in domestic gas boilers, and most current ecoTEC plus and exclusive models still use the same philosophy 20 years on. Stainless steel costs more than aluminium but tolerates poor system water better and lasts longer, which is why Vaillant boilers from the late 2000s are still working today on properties that haven’t always had the inhibitor maintenance they should have.

A well-maintained ecoTEC plus from 2010 isn’t unusual — I service them every year. They’re quieter than most boilers (most of the ecoTEC plus range carries Quiet Mark accreditation), modulate well, and the build quality is properly engineered.

Older Vaillant boilers, model by model

I routinely repair the ranges below. If you’ve been told yours needs replacing — talk to me first.

ecoTEC plus and ecoTEC pro (roughly 2007–2014 generation)

The stainless steel heat exchanger on the ecoTEC plus is excellent and rarely the reason for failure. What does fail with predictable regularity on this era is the PCB. Vaillant PCBs from this window have a known electronics weakness and typically start playing up around the 9–10 year mark. Vaillant addressed it on later boards and on the current plus and exclusive ranges (the ecoTEC exclusive with Green iQ wasn’t launched until 2015 and doesn’t suffer the same issue), but if your plus or pro is from that 2007–2014 window and behaving intermittently, the PCB is the first place I look.

A replacement PCB on an older ecoTEC is far cheaper than a full boiler replacement and gives you another 8–10 years easily. It matters because the PCB failure on older Vaillants almost always shows up disguised as something else — see the fault-code section below, particularly the F.61/F.62 entry. I’ve seen homeowners pay for new gas valves they didn’t need, because the symptom wasn’t recognised.

ecoFIT pure

Vaillant’s more recent budget range, with an aluminium heat exchanger. The exchanger needs proper system water quality to last — inhibitor checked annually, magnetic filter fitted from new. Most faults I see on ecoFIT pure are pressure-sensor-related (showing as F.22 or F.75) rather than the boiler itself. The Quiet Mark accreditation is genuine; these are quiet boilers.

ecoMAX Pro and ecoMAX Plus (the pre-ecoTEC generation)

Where parts are still available, I service these. Some are no longer economically repairable — I’ll tell you plainly which is which.

Common Vaillant fault codes

Vaillant uses an F.xx code system across the ecoTEC range. The ones I see most:

F.22 — low water pressure

Often a slow leak, a passing pressure-relief valve, or a flat expansion vessel. Repeatedly topping up adds fresh oxygenated water and speeds internal corrosion. I find the cause rather than just refilling.

F.28 / F.29 — ignition and flame-loss faults

F.28 is the boiler failing to ignite; F.29 is flame loss during operation. The code points at the ignition system, but the underlying cause is often somewhere else. The most common hidden cause on older Vaillants is a blocked condensate trap — the syphon at the bottom of the boiler that collects acidic water from the heat exchanger and drains it away. If it blocks (silt, soot, burned dust, years of build-up), condensate backs up inside the boiler and interferes with combustion: the ignition and flame-detection systems can’t operate reliably with a flooded combustion chamber, and you get F.28 or F.29 lockouts.

Cleaning the trap should be a routine annual job — it twists out from underneath the boiler and pulls downwards. But two recurring install patterns make it inaccessible. On older installs, the original pipework (gas, water feeds, flow and return) was run directly underneath the trap, preventing it being pulled down, or right across its body so it can’t be twisted free at all — the trap is there but can’t be reached without dismantling unrelated pipework. On newer installs, the opposite: the rigid plastic condensate drain runs straight into the trap with no flexible section or union, so the trap can’t come out without cutting and re-piping the drain. Either way the trap doesn’t get cleaned, the blockage builds for years, and one cold morning the boiler throws an F.28 or F.29 that looks like ignition failure but is a flooded combustion chamber. The fix is to clean or replace the trap and — where the install made it inaccessible — re-route the surrounding pipework so future servicing is straightforward. Not about blaming the previous installer; about making sure your boiler can actually be serviced properly next time.

The air the boiler breathes

This one isn’t widely discussed but matters more than people realise. A modern condensing boiler draws combustion air from outside through the flue, and that air isn’t filtered — whatever’s in the outside air goes into the combustion chamber and gets burned. In a normal urban or suburban setting that’s fine. But if the boiler faces a construction site, a neighbour’s extension, heavy traffic disturbing road dust, or a flue terminal that collects debris (pollen, leaves, soot from a nearby chimney), all of that gets pulled into the combustion air. The dust burns alongside the gas and the residue settles in the condensate trap. A boiler next to building work for six months can block its trap far quicker than the same boiler in clean air — the code shows F.28 or F.29, but the root cause is the dust it was forced to breathe. If your Vaillant has started misbehaving and there’s been building work nearby in the last year or two, mention it when you call — it changes where I look first.

Other genuine causes of F.28/F.29: condensate pipe frozen externally (common in cold snaps if it exits the building unlagged), gas supply restriction at the meter or governor, a worn ignition electrode or flame-detection lead, and on the 2007–2014 PCBs, sometimes the board itself.

F.20 — safety switch-off, temperature limiter (overheat)

A system problem more often than a boiler one — flow restriction, sludge, dead pump, closed valve.

F.25 — flue gas temperature too high

STB (flue gas safety thermostat) related. Sometimes the STB itself, sometimes the harness, sometimes the cause is upstream.

F.27 — flame detected when there shouldn’t be one

A genuine safety fault — don’t reset and hope.

F.61 / F.62 — gas valve fault. Read this one carefully.

The code says “gas valve”, so the instinct is to quote a new gas valve. In my experience, 99% of the time on older ecoTEC plus and pro boilers the fault is actually the PCB, not the gas valve. The PCBs on the 2007–2014 generation have an internal low-voltage section that supplies stable DC to the sensors and the gas valve control circuit. As the PCB ages, that section deteriorates and stops delivering the steady reference voltage the sensors need. The sensors then return implausible readings; the PCB can’t reconcile them with what the gas valve should be doing, and throws an F.61 or F.62 “gas valve fault”. The valve is fine. Replacing it solves nothing and costs around £300–£400 in parts that weren’t needed.

The quick diagnostic: watch the flow temperature on the display while the boiler runs. On a healthy Vaillant it’s stable, or rises and falls smoothly with demand. On one with a failing PCB it jumps around erratically — sitting at 55, jumping to 65, dropping back, jumping again, with no real change in demand. (Exact numbers don’t matter; the erratic jumping is the flow sensor being fed unstable voltage by the failing PCB.) See that pattern and the PCB is the fault, not whatever the code blames. Replacing the PCB on these is a standard job for me — cheaper than a new gas valve, cheaper still than a new boiler.

F.75 — widely misdiagnosed

The code reads as “pump pressure” or “pump fault”, so the instinct is to quote a new pump. In my experience on ecoTEC plus and pro boilers, well over 90% of F.75 faults aren’t a pump problem at all — they’re a blocked digital pressure sensor. The ecoTEC uses a digital pressure sensor to assess both the static system pressure and whether the pump is working: at startup the PCB fires the pump for two seconds and watches for a change in the pressure reading between off and on. If the pressure climbs, the pump’s working; if it doesn’t, F.75.

What goes wrong: over time, debris in the system water blocks the sensing element. Stuck, the sensor reports a fixed value in the normal range (0.8–3.0 bar), so the PCB sees a “valid” pressure and doesn’t suspect it — but when the pump fires for its check, that reading never changes, so the PCB concludes the pump isn’t moving water. F.75 displayed; customer quoted for a pump. In reality, a new pressure sensor — much cheaper than a pump — solves it.

There’s a design-fault element: the sensor sits where debris is most likely to collect. A better position would be vertical, on the return before the pump, where debris drops out of the flow rather than settling in. And there’s a water-cleanliness element — dirty system water on an old install is the underlying cause. Worth noting: a magnetic filter alone doesn’t prevent this. I’ve seen plenty of installs with a properly fitted magnetic filter where the sensor still blocked, because magnetite isn’t the only debris in older systems. What works is a proper system flush and treatment before the install, paired with a mesh-type filter alongside the magnet. Because these sensors are so prone to it, I carry spares in the van as standard — F.75 on an older Vaillant is usually a same-visit fix.

F.83 / F.84 / F.85 — water temperature sensor issues

Cheap parts, quick fixes.

If your Vaillant is showing a code and you’d like a second opinion before booking anyone — call 07864 757929. Happy to talk through what you’re seeing on the display.

aroTHERM plus — air source heat pumps

The aroTHERM plus is Vaillant’s flagship monobloc air source heat pump and one of the best available on the UK market — worth a proper paragraph rather than a footnote. It uses the natural refrigerant R290 (propane), with a Global Warming Potential of just 3, against 675 for R32 and 2,088 for the older R410a some manufacturers still use. Beyond being far better environmentally, R290 allows a higher flow temperature: the aroTHERM plus delivers heating water up to 75°C, so it can work with existing radiators in a retrofit without forcing you to upsize them. Most R32 heat pumps cap at 55°C, which is why so many retrofits underperform — the property’s radiators were sized for a 70°C+ boiler and don’t put out enough heat at 50°C.

Outputs: 3.5, 5, 7, 10 and 12 kW. SCOP up to 5.03 — for every 1 kW of electricity, up to 5 kW of heat. Operating range -25°C to +46°C ambient. Sound power as low as 54 dB(A), Quiet Mark accredited across most of the range. My Advance Installer status extends to renewables, so I can offer up to a 7-year manufacturer warranty on the aroTHERM plus when fitted with a Vaillant uniSTOR cylinder and registered through Advance.

For MCS-grant installs (the £7,500 Boiler Upgrade Scheme), the work has to be routed via an MCS-accredited umbrella partner — I offer this with the partner’s cost passed on at cost, and I also offer non-grant installs at lower total cost where the property doesn’t qualify or you don’t need the grant. Full picture on my Heat Pump Repair and Installation Luton page. The engineer who knows your ecoTEC plus inside out is the same one who’s factory-trained on the aroTHERM plus — when the day comes to think about renewables, in two years or twelve, you won’t be starting over with a company that doesn’t know your system.

The Vaillant Advance Installer warranty, in practice

I’m a member of Vaillant’s Advance Installer scheme. In practical terms for you:

• Up to 10 years’ manufacturer warranty on ecoTEC plus and exclusive when installed with the Vaillant Advance Boiler Protection Kit (a Vaillant-specified magnetic filter on the return) and registered with Vaillant within 30 days.
• Up to 7 years’ manufacturer warranty on ecoTEC pro and ecoFIT pure when registered through Advance.
• Up to 7 years’ manufacturer warranty on the aroTHERM plus heat pump when paired with a Vaillant uniSTOR cylinder and registered.
• I handle the registration — you don’t have to chase paperwork.
• The warranty is direct from Vaillant: they send their own service engineer if something goes wrong under warranty, independent of whether I’m still around (I will be, but the cover isn’t dependent on it).

To keep the warranty valid you need an annual service from a Gas Safe engineer (me, or anyone else with Vaillant training, is fine). I send a reminder.

Why I so often recommend Vaillant

Clients often ask which brand I’d choose. I’ll always say “the right boiler for your property”, because no brand is the answer to every job. But a few reasons Vaillant is so often the answer:

The service life genuinely exceeds the warranty period every time, provided the boiler is maintained correctly — a Vaillant on annual service is still working long after the 10-year warranty has expired.

Parts availability is the best of any brand I work on. Vaillant’s UK parts network means most parts I need are stocked by the local merchants I use, available same-day. That matters when you’ve got no heating or hot water and the alternative is waiting three days for a part from a central warehouse.

The warranty and customer service from Vaillant are decent. Not perfect — no manufacturer is — but the process for end customers is straightforward, the engineers Vaillant send out know what they’re doing, and there’s no fight to get cover applied when something goes wrong inside the warranty period.

I’ve installed over 100 Vaillant boilers and I know the range inside out — every fault code, every quirk, every common failure mode. Call me with a Vaillant problem and you’re talking to someone who’s seen that specific issue before, usually many times. None of which means I won’t recommend a different brand if it’s the better fit — I install Worcester and Ideal too, where one of those suits the property better.

What I charge

I work on clear pricing rather than fixed-fee guesses. Every property is different, so a proper quote needs me to see the job. Broadly:

Diagnostic visit and repair — charged at my hourly labour rate. Most domestic Vaillant repairs are done inside a single visit. Parts at trade price plus a fair, visible mark-up, itemised on the invoice. A PCB replacement on an older ecoTEC plus, for example, is a half-day job once the diagnosis is confirmed.

Annual service — also at hourly rate. A proper Vaillant service includes full combustion analysis on a calibrated flue gas analyser, gas pressures checked at meter and boiler, condensate trap clean (where it can be accessed — see the F.28 section above), magnetic filter clean, expansion vessel pressure check and re-charge if needed, inhibitor strength test, visual inspection of flue and seals, the full Vaillant service log written up, and Advance scheme renewal where applicable.

Powerflush on a typical 3-bed — one day on site, plus system cleaner and fresh inhibitor (Adey, Fernox or Sentinel only). If the flush turns up a faulty radiator valve, a tired drain-off or a corroded pipe section, I’ll show you and quote those parts separately rather than hide them in a flat fee. Detail on my Powerflush page.

Like-for-like Vaillant boiler swap — depends on the model, property and existing pipework. Rough guide:

• ecoTEC pro combi swap — typically £2,500 to £3,100 all in
• ecoTEC plus combi swap — typically £2,800 to £3,400 all in (with the Advance Boiler Protection Kit for the 10-year warranty)
• ecoTEC exclusive combi swap — typically £3,300 to £4,000 all in

Each figure covers the boiler, the Advance Boiler Protection Kit where required, a flue kit, system cleaner and fresh inhibitor, new isolation valves and a scale reducer where Luton’s hard water needs it, gas commissioning and Building Regulations notification. I quote each one after seeing the property — no guess-and-add-later pricing. You get the Vaillant manufacturer warranty registered through Advance, my 24-month workmanship warranty on top, and the same engineer answering the phone if anything’s wrong over the next decade.

The fault is rarely the boiler

Most boiler problems are system problems. The boiler is the most visible part of the heating, so it gets blamed when the actual fault is elsewhere — sludged pipework, a tired pump, an undersized or flat expansion vessel, the wrong inhibitor, or no inhibitor at all.

The F.61/F.62 PCB story above is one example; the F.75 pressure-sensor story is another. The expansion vessel matters too — the factory pre-charge isn’t always right for a property’s static head, and the wrong vessel pressure gives repeated F.22 lockouts, repeated re-pressurising, and accelerated corrosion of internal components. I check and recharge the vessel on every Vaillant service.

Water quality matters more on Vaillant than on most brands, because the stainless steel heat exchanger across the ecoTEC plus range is durable but not invincible. I only use Adey, Fernox or Sentinel inhibitor, never the cheap own-label products some merchants push, and I test inhibitor strength on every service.

For the wider picture on diagnostic process, magnetic filters, inhibitor quality and the rest, see my Boiler Repair Luton page.