Boiler
E10
The E10 error code on a Viessmann boiler indicates a problem with the boiler’s water pressure or flow — specifically, the safety pressure switch has tripped. It’s a common fault, but because it involves your gas boiler’s safety systems, it must be treated seriously.
What does this error mean?
E10 signals that the boiler’s minimum pressure switch has detected pressure that is too low for the boiler to operate safely. Viessmann boilers are designed to shut down automatically when pressure drops below a safe threshold (typically below 0.5 bar) to prevent damage to the heat exchanger and internal components. The boiler will not fire again until the underlying pressure issue is resolved and the system is within the correct operating range (usually 1–1.5 bar when cold).
Est. repair cost
£150–£300 for a Gas Safe engineer call-out, diagnosis, and repair (pressure switch or expansion vessel). Re-pressurising the system yourself costs nothing if no parts are needed.
🔍 Likely causes
🛠️ Step-by-step fix
Check the pressure gauge on your boiler. It should read between 1.0 and 1.5 bar when the system is cold. If it reads below 1 bar, low pressure is the likely cause.
Inspect all visible radiators, pipework, and the area directly beneath the boiler for signs of dripping water or damp patches. A visible leak must be fixed by a Gas Safe engineer before re-pressurising.
If there is no visible leak and the pressure is low, use the filling loop (a small braided hose or lever-tap beneath your boiler) to slowly top up the system pressure to approximately 1.2–1.3 bar. Stop immediately if you reach 1.5 bar.
Once pressure is restored to the correct level, press and hold the reset button on your Viessmann boiler (usually marked with a flame or ‘R’ symbol) for 3–5 seconds until the display clears.
Monitor the boiler over the next 24–48 hours. If pressure drops again, you have a leak or a failed expansion vessel — do not keep topping up without investigating the root cause.
Do not attempt to access internal boiler components, adjust the gas supply, or interfere with the pressure switch or expansion vessel yourself. This requires a Gas Safe registered engineer.
📞 When to call a professional
Call a Gas Safe registered engineer immediately if you can see a water leak, if the pressure drops repeatedly after re-pressurising, or if the boiler displays E10 even when the pressure gauge reads within the correct range (suggesting a faulty pressure switch). When you call, tell the engineer: ‘My Viessmann boiler is showing error code E10, I’ve checked the pressure and [state what you found]’ — this helps them arrive prepared with the right parts.
⚖️ Repair or replace?
A pressure switch replacement or expansion vessel re-charge typically costs £150–£300 with a Gas Safe engineer, depending on your location and boiler model. If your Viessmann boiler is under 10 years old and otherwise reliable, repair is almost always the right call — Viessmann boilers are premium units with long lifespans. If it’s over 15 years old and requiring repeated repairs, replacement with a modern Viessmann Vitodens or equivalent A-rated condensing boiler (£2,000–£3,500 installed) is worth considering for efficiency savings.