Vaillant boiler fault codes, explained
Your Vaillant ecoTEC plus or pro is showing a code on the display. Most are straightforward once you know what they mean — and knowing whether you can act yourself or need a Gas Safe engineer can save you time and keep you safe.
Before you do anything: safety first
If you can smell gas, do not attempt a reset. Leave the property, do not use light switches, and call the National Gas Emergency Service on 0800 111 999 (free, 24 hours).
For fault codes with no gas smell: a single reset is reasonable. Press the reset button, wait a couple of minutes, and see if the boiler fires. If the same code reappears, stop resetting. Repeated resets on a genuine fault can damage components and, on ignition or gas valve faults, carries a safety risk. One reset, then call an engineer.
Common Vaillant fault codes at a glance
| Code | What it means | What to do |
|---|---|---|
| F.22 | Water pressure too low — system needs repressurising | Homeowner: top up via filling loop to 1—1.5 bar, then reset. If pressure drops again within days, there is a leak — call an engineer |
| F.27 | Flame detected when burner should be off — gas solenoid valve or PCB fault | Engineer required. Do not reset repeatedly |
| F.28 | Ignition failure — boiler attempted to light but failed | Check gas supply (do other appliances work?). In cold weather, check condensate pipe for ice. One reset. If it persists, call an engineer |
| F.29 | Flame loss after ignition — flame went out mid-cycle | Same checks as F.28. One reset. Persistent F.29 needs an engineer |
| F.53 | Combustion regulation fault — gas-air ratio outside safe limits | Check gas supply. In winter, check condensate pipe. One reset. Requires an engineer if it persists — combustion faults should not be left |
| F.61 | Gas valve fault — valve failed to open correctly | Engineer required. Do not reset repeatedly |
| F.62 | Delayed gas valve shut-off — gas detected when burner should be off | Engineer required. Switch the boiler off at the programmer until inspected |
| F.75 | No pressure change detected when pump starts — pump failure or pressure sensor fault | Check system pressure (1—1.5 bar). If pressure is correct, the pump or sensor needs an engineer |
| S.53 | Status code: waiting period due to excessive flow/return temperature spread | Not a fault in isolation — boiler is protecting itself. Can indicate air in the system or a circulation issue. Bleed radiators. If it recurs, have an engineer check pump speed and system balance |
F.22 — low water pressure
This is the most common Vaillant fault and one of the few you can safely sort yourself. The boiler needs water pressure between 1 and 1.5 bar (the green zone on the pressure gauge). If it has dropped below that — often caused by a small system leak or normal pressure loss over time — the boiler locks out to protect itself.
How to repressurise: locate the filling loop (usually a flexible braided hose underneath the boiler with two valves), slowly open both valves until the pressure gauge reads around 1.2 bar, then close both valves. Press reset on the boiler.
If you are not sure how to do this, there is a separate guide on how to repressurise your boiler. If pressure keeps dropping within a few days, there is a leak somewhere — that needs an engineer.
F.28 and F.29 — ignition and flame failure
These two codes are related. F.28 means the boiler tried to ignite and could not establish a flame. F.29 means it lit briefly but the flame went out.
Common causes include:
- No gas supply (check whether the gas meter is working and other appliances are firing)
- Frozen condensate pipe (common in cold snaps — the condensate pipe runs outside and can ice over)
- Faulty ignition electrode or lead
- Flue blockage
In winter, a frozen condensate pipe is the most frequent culprit. You can carefully thaw it with warm (not boiling) water poured over the external section. Once thawed, reset the boiler. If the code comes back, or if you are unsure where the condensate pipe runs, call an engineer.
F.75 — pump or pressure sensor fault
F.75 means the boiler’s pressure sensor did not detect a change in pressure when the pump started. This could be low system pressure (check the gauge — if it is below 1 bar, repressurise first) or a failing pump or pressure sensor.
Unlike F.22, F.75 often points to a component fault rather than low pressure alone. If the pressure looks fine and the code keeps returning, it needs a professional diagnosis.
F.27 and F.62 — gas valve issues
Both of these relate to the gas valve behaving unexpectedly. F.27 means flame was detected when the valve should be fully closed. F.62 means the valve was slow to close after the burner shut down.
Neither is a homeowner fix. The gas valve is a safety-critical component. If you see either of these, switch the boiler off and call a Gas Safe engineer.
F.53 — combustion regulation fault
The boiler monitors its own combustion and will lock out if the gas-air mixture falls outside safe parameters. Causes include low gas pressure at the meter, a partially blocked flue, or a faulty gas valve.
One reset is worth trying after checking gas supply and the condensate pipe. If it recurs, this is not a fault to leave — have it looked at promptly.
When to call an engineer straight away
Call a Gas Safe registered engineer without resetting if you see:
- F.27 or F.62 (gas valve safety faults)
- Any fault code combined with a gas smell
- A code that returns immediately after resetting
- F.28 or F.29 with no obvious cause (not a frozen condensate pipe, gas supply confirmed fine)
BASI Heating: Vaillant Advance accredited, Gas Safe registered
BASI Heating is a Vaillant Advance accredited installer (Gas Safe #623525) covering Yorkshire. We carry common Vaillant parts on the van, which means many repairs are completed in a single visit.
Same-day boiler repair is available from £80 for the first hour, with fixed pricing so you know the cost before we start. No salesmen, no upsell — just a diagnosis and a straight quote.
The best way to avoid fault codes is a yearly boiler service, which catches worn components before they cause a breakdown. Vaillant recommends annual servicing to keep the warranty valid too.
If your ecoTEC is displaying a code and you are not sure what to do next, call us and we will talk you through it.