Chaffoteaux 110 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 110 fault code mean?
Fault code 110 (displayed as '1 10' on some models) indicates that the boiler's flow temperature probe — an NTC thermistor that continuously measures the temperature of water leaving the heat exchanger — has been detected as damaged or has failed entirely. Because the boiler relies on this sensor to monitor water temperature and prevent overheating, it cannot operate safely without a reliable reading and will lock out until the issue is resolved. This is a sensor fault, not simply an overheating event; do not confuse it with code 101 (overheat lockout), though the two are related. Note that fault code numbering varies across Chaffoteaux ranges: the '1 10' designation is confirmed for the Expert Control range. If your model is a Pigma, Britony, Urbia, or an older variant, verify the code against your own manual or call a Gas Safe engineer with your exact model name and code.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Failed or degraded NTC flow probe Common
The NTC thermistor itself has reached the end of its service life, suffered corrosion on its connector pins, or sustained physical damage. As the component ages, its resistance characteristics drift, causing the PCB to receive readings it cannot trust. This is the most direct cause and is what the fault code is specifically designed to flag.
- Wiring or connector fault between probe and PCB Common
Even when the probe element itself is intact, a corroded terminal, a chafed cable, or a loose push-fit connector can cause the same erratic or open-circuit signal that triggers fault 110. This is particularly common in older installations where the loom has been disturbed during previous servicing.
- Circulator pump failure causing overheating stress on the probe Sometimes
When the pump slows down or fails, water sits in the heat exchanger longer than intended and gets much hotter than normal. Repeated exposure to these temperature spikes can degrade the probe prematurely, causing it to fail and trigger the fault.
- Limescale or sludge restricting heat exchanger flow Sometimes
In hard-water areas, scale builds up on the internal surfaces of the heat exchanger, reducing thermal transfer and causing localised hot spots. Similarly, sludge accumulation from an unflushed system restricts circulation. Both conditions stress the probe over time and can eventually damage it.
- Air lock in the heating circuit Rare
Trapped air in the pipework or heat exchanger disrupts smooth water flow. The resulting hot spots can damage the probe or produce erratic readings that the boiler interprets as a sensor fault.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your Chaffoteaux boiler (usually a flame symbol with a line through it, or a dedicated reset button depending on model). Press and hold for the time specified in your user guide, then wait two to three minutes for the boiler to attempt a restart. If the fault code returns immediately or after a short run, do not keep resetting — repeated resets will not fix a damaged probe and can mask underlying problems.
- Bleed your radiators to release trapped air DIY safe
Turn off the heating and let the system cool slightly. Starting on the ground floor, use a radiator bleed key to open each bleed valve a quarter-turn until water (not air) escapes, then close it. Work your way upstairs. Once done, check your system pressure at the boiler gauge — it should read between 1 and 1.5 bar when cold. If pressure has dropped below 1 bar, top it up via the filling loop before restarting.
- Check and restore system pressure if low DIY safe
A system pressure below 1 bar can contribute to poor circulation and overheating. Attach the filling loop hoses (if not permanently connected), slowly open both valves, and watch the pressure gauge rise to around 1–1.5 bar, then close the valves. Do not overfill above 2 bar. If the system repeatedly loses pressure, inform the engineer — there may be a leak elsewhere.
- Have a Gas Safe engineer test the NTC probe resistance Gas Safe engineer
An engineer will disconnect the probe connector and use a multimeter to measure the thermistor's resistance at a known temperature, comparing it against the manufacturer's specification curve. A reading that is open-circuit, short-circuit, or wildly outside the expected range confirms probe failure. This step requires opening the boiler casing and working on electrical components — not a DIY task.
- Have a Gas Safe engineer replace the NTC flow probe if confirmed faulty Gas Safe engineer
Replacement involves draining down or isolating the relevant circuit, removing the old probe from its pocket in the flow pipework, fitting a new genuine or compatible NTC thermistor, and re-testing. The engineer should clear the fault code and run the boiler through a full heating cycle to confirm a stable temperature reading.
- Have the circulator pump inspected and replaced if necessary Gas Safe engineer
If the probe checks out but the fault recurs, a sluggish or failing pump is the next suspect. An engineer can check pump speed and output pressure. A pump that cannot circulate water at the correct rate will cause the heat exchanger to overheat, stressing any new probe fitted and eventually causing the same fault again.
- Arrange a system power flush if sludge or scale is suspected Gas Safe engineer
If cold spots on radiators, discoloured water at bleed valves, or a history of circulation problems suggest sludge, a power flush should be carried out before or alongside the probe replacement. A power flush uses specialist equipment to push high-velocity water and cleaning chemicals through every part of the circuit, dislodging and expelling debris. Adding an inline magnetic filter afterwards helps prevent recurrence.
- Call a Gas Safe registered engineer if the fault persists or you are unsure at any stage Gas Safe engineer
Fault 110 ultimately requires an engineer to diagnose and resolve. If you have attempted a single reset and bled the radiators without success, book a qualified engineer rather than continuing to reset the boiler. Always ask to see their Gas Safe ID card before work begins — you can verify registration at gassaferegister.co.uk.
Parts you may need
- NTC flow temperature thermistor probe · from £25
- Probe connector / wiring harness · from £18
- Circulator pump (compatible replacement) · from £85
- Magnetic system filter (e.g. Fernox TF1 or equivalent) · from £55
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£380, depending on the underlying cause.
Frequently asked questions
Can I fix a Chaffoteaux 110 fault code myself?
There is very little a homeowner can safely do beyond a single boiler reset and bleeding the radiators to clear any trapped air. The probe itself sits inside the boiler casing connected to the PCB, and testing or replacing it involves working on electrical and plumbing components — all of which legally require a Gas Safe registered engineer in the UK. Attempting it yourself could void any remaining warranty and, more importantly, create a safety risk.
How much does it cost to fix a Chaffoteaux 110 fault?
For most people, the repair bill falls between £120 and £380. If the fault is simply a failed NTC probe (the most common cause), expect to pay roughly £100–£200 all in — a modest part cost plus an hour or so of labour. If the root cause is a failing pump or a sludged-up system requiring a power flush, costs typically rise to £250–£500. A heat exchanger replacement is a much rarer outcome but can cost £400–£700 in parts alone; at that point, and if the boiler is over 12–15 years old, it is worth getting a new boiler quote for comparison.
Why does my Chaffoteaux keep showing code 110 after resetting?
If the fault returns immediately or within a short time of resetting, the probe has almost certainly failed permanently and needs replacing rather than resetting. Persistent recurrence can also indicate an underlying circulation problem — a weak pump or restricted heat exchanger — that keeps stressing the probe. Repeated resets without diagnosis will not resolve the underlying fault and may mask a worsening problem, so book an engineer if the code returns more than once.
Is fault code 110 the same on all Chaffoteaux boilers?
Not necessarily. Chaffoteaux has produced several boiler ranges over the years — Expert Control, Urbia, Britony, Pigma, Nectra, and others — and fault code formats can differ between them. The '1 10' flow probe fault is confirmed for the Expert Control range. On other models the same underlying fault may appear under a different code number. If you are unsure, check your boiler's own user manual or call a Gas Safe engineer quoting your exact model name and the code displayed.