Potterton E110 fault code: the safety thermostat has tripped

What does the Potterton E110 fault code mean?

The Potterton E110 fault code means the boiler overheated and its safety thermostat tripped, locking the boiler out to protect it. Heat was not moving away from the heat exchanger fast enough, or the thermostat that watches for exactly that has failed. Try to read it as the boiler doing its job: it noticed it was running too hot and stopped, rather than carrying on.

Potterton and Baxi are part of the same group and share this code set, so E110 is the same overheat lockout on both. The codes either side of it are the ones people mix it up with: E119 is system pressure too low, E125 is a primary water circulation fault and E133 is an ignition fault. Wording varies a little between the Promax, Gold, Titanium and Assure ranges, so check the fault-code list in your own boiler's manual to confirm what your model shows.

Some Potterton displays are only two characters wide, so a three-digit code is shown in two parts rather than all at once. E133, for example, may flash as E1 alternating with 33. If your display is splitting the code up, or dropping the letter E, read it against the list in your own manual before you settle on which code you have.

Potterton does not publish a public fault-code list, which is worth saying plainly because it explains why E110 is so hard to look up. The old Potterton consumer site now redirects to Baxi, whose homeowner help covers only a handful of Baxi codes and does not include E110. The full table sits in Baxi's professional technical-support pages and in the installation and service manual that came with the boiler, written for installers rather than for the person standing in front of it.

Key facts

The quick version, before the detail.

• What it means: the boiler overheated and the safety thermostat tripped, so the boiler locked out.
• DIY fixable? No. You can read the pressure gauge, check the radiator valves are open, look and listen with the casing closed, and reset once. Everything else is inside a gas appliance.
• Do not sit there resetting it. Repeatedly clearing an overheat lockout hides the real fault and can damage the heat exchanger.
• Usual causes: a jammed pump, air trapped in the circuit, sludge or scale restricting flow, or radiator valves turned right down. The safety thermostat itself can also fail.
• Not the same code as E119 (system pressure too low, below about 0.5 bar) or E125 (primary water circulation fault).
• Seen on Potterton boilers that use the E-prefixed codes, most often the Promax and Gold ranges. Check your own manual for your model's exact wording.
• Not published by the manufacturer: potterton.co.uk redirects to Baxi, there is no public fault-code page, and the definition sits in the installer manual.
• Gas emergency? Call the National Gas Emergency Service on 0800 111 999 if you smell gas or a carbon monoxide alarm sounds.
• Smart Plan boiler and central heating cover is a service plan, not insurance, and it is for future breakdowns rather than a fault your boiler is already showing.
• Using a module starts a 12-month agreement period the first time you use a service. There is a 14-day cooling-off period, but it ends once a service is carried out, and leaving early after that costs the remaining months or 75% of the outstanding balance.

Why does the Potterton E110 code appear?

Potterton prints no cause list under E110, and the code itself narrows it to two things. Either the boiler genuinely overheated because heat could not move away from the heat exchanger quickly enough, or the safety thermostat that detects an overheat has failed and is reporting one that never happened.

In practice, most E110 lockouts come down to poor circulation. A jammed or failed pump means the heat is not being carried away at all. Air trapped in the circuit creates pockets that stop water flowing freely. Sludge, the black gritty build-up that collects over years, restricts flow through radiators and pipework. Scale in the heat exchanger holds heat in one spot instead of moving it on. Closed or stuck valves do the same thing from the other end of the system. Those are also what sits behind E125, the circulation fault code, which is why the two codes often share a root cause.

One thing to rule out: low pressure is not E110. Potterton gives low system pressure its own code, E119, which shows when the pressure drops below about 0.5 bar. Glancing at the gauge is still worth doing, because low pressure and poor circulation travel together, but a low reading on its own points at E119. The table below runs through the likely causes and who can safely deal with each one.

E110 causes and what to do about each one

What can I safely check myself?

There is no safe DIY repair for E110, because every diagnostic step sits behind the casing of a gas appliance. Four checks are worth making before you pick up the phone, and an engineer will ask you about them anyway.

1. Read the pressure gauge. Cold, with the boiler not running, most sealed heating systems sit around 1.0 to 1.5 bar. Below about 0.5 bar a Potterton will normally show E119 instead, and above 2.5 bar when the system is hot is too high. Note what yours reads and pass it on.

2. Look and listen, with the casing left closed. Are the radiators heating? Are any cold, or cold across the top? Any banging, kettling or gurgling while the boiler runs? Is the room thermostat or programmer actually calling for heat? Never remove the boiler casing.

3. Check the radiator valves are open. If most of the radiators in the house are turned right down, the boiler has nowhere to send its heat. Opening a couple fully is safe, and it sometimes stops the lockout repeating.

4. Reset once, and only once. The reset control is not the same across the Potterton range: some models use a button held for a few seconds, others use the mode selector knob turned round to a reset position. Follow the reset instructions in your own user guide rather than advice written for a different boiler.

Then stop. Resetting again does nothing about whatever made the boiler overheat, repeated resets can damage the heat exchanger, and the safety thermostat is the last line of protection you have. If E110 comes back, that is the point to book an engineer.

When to call a Gas Safe registered engineer

Call an engineer if E110 returns after a single reset, if it keeps appearing over days or weeks, or if the boiler locks out within minutes of firing. Everything from here means removing the casing from a gas appliance: testing and replacing the safety thermostat once the boiler is cool, testing the temperature sensors, checking the pump, flushing the primary circuit, and replacing the control board if everything else tests good.

You can book a one-off repair with us without joining a plan, or call 0333 772 6247. One-off repair visits run Monday to Friday, 09:00 to 17:00. A £95 call-out fee applies and is paid in advance, and the engineer diagnoses the fault and tells you what is needed and what it costs before any work goes ahead. One-off repairs are not covered by a workmanship guarantee. We work with a national network of thousands of Gas Safe registered engineers, and we aim to get an engineer out to you within two working days, which is a target for attendance rather than a promise of a finished repair.

A Smart Plan boiler and central heating module is a different thing, and it is worth being straight about what it does. Cover is for future breakdowns, not a fault your boiler is already showing: an E110 on the display today counts as a pre-existing fault, so a new plan would not pay for this one, and a one-off repair is the route for it. For the next fault, the module covers parts and labour up to £500 per 12-month period if your boiler is under 7 years old, or up to £200 if it is over 7, and you pay anything above that limit yourself. On a job like a new pump, a power flush or a heat exchanger, that gap can be real. Where our cover terms treat equipment as beyond economic repair, which includes a failed control board or heat exchanger, the plan pays a contribution towards a replacement instead of funding a repair.

The rest of the small print, in one place. A £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, if the engineer cannot get access, and for early annual-service requests. Your cover itself applies from the start of your agreement: the first 30 days are a call-out fee window, not a gap in cover. Cover-plan call-outs run Monday to Friday, 08:00 to 18:00. Outside those hours you are only seen sooner for a genuine emergency breakdown as set out in your terms, so a Friday-evening or weekend fault can wait until Monday. Using a module starts a 12-month agreement period from the first time you use a service. There is a 14-day cooling-off period, but it ends the moment a service is carried out, and leaving early after that costs the remaining months or 75% of the outstanding balance. Smart Plan is a service plan, not insurance: it arranges and funds covered repairs up to the limits on your plan rather than paying out a cash sum. It comes from UK Boiler Company Ltd.

One safety note. Potterton boilers are gas appliances, and E110 is an overheat lockout rather than a gas fault. But if you ever smell gas or suspect carbon monoxide, do not wait for an engineer: call the National Gas Emergency Service on 0800 111 999 straight away, open the windows, and do not touch electrical switches.

Potterton E110 fault code FAQs

E110 keeps coming back? Book a Gas Safe registered engineer.

Book a one-off repair and we will arrange a Gas Safe registered engineer to test the safety thermostat and the system behind it. One-off repair visits run Monday to Friday, 09:00 to 17:00, a £95 call-out fee applies and is paid in advance, and the engineer tells you what is needed and what it costs before any work goes ahead. One-off repairs are not covered by a workmanship guarantee. We aim to get an engineer out to you within two working days, which is a target for attendance rather than a promise of a finished repair. A Smart Plan boiler and central heating module is for next time rather than this one: cover is for future breakdowns, not a fault your boiler is already showing, so an E110 on the display today counts as a pre-existing fault. It funds covered repairs up to £500 per 12-month period for a boiler under 7 years old, or up to £200 if it is older, and you pay anything above that limit yourself. Where the terms treat equipment as beyond economic repair, which includes a failed control board or heat exchanger, it pays a contribution towards a replacement instead. Cover-plan call-outs run Monday to Friday, 08:00 to 18:00, unless it is a genuine emergency breakdown. A £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, no-access visits and early annual-service requests, and your cover itself applies from the start of your agreement. Using a module starts a 12-month agreement period from the first time you use a service; there is a 14-day cooling-off period, which ends the moment a service is carried out, and leaving early after that costs the remaining months or 75% of the outstanding balance. Smart Plan is a service plan, not insurance. Call 0333 772 6247.

Helpful links

• All Potterton fault codes
• Baxi E110 fault code
• No heating? Book a repair
• Boiler repair
• Boiler & central heating cover
• More boiler guides on the blog
• Check an engineer on the Gas Safe Register