Chaffoteaux 116 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 116 fault code mean?
Fault code 116 on Chaffoteaux boilers signals that the manual-reset safety thermostat on the underfloor heating circuit has tripped open. This thermostat acts as a last line of defence against overheating — it cuts the electrical circuit and triggers a boiler shutdown when the underfloor circuit temperature climbs beyond a safe threshold (typically around 55–60°C). Because this is a manual-reset device, the boiler will remain locked out until the thermostat is physically reset at the manifold or control box, and the underlying cause is identified. The closely related code E30 (seen on older Chaffoteaux & Maury models without a numeric display) describes the same condition. Newer display-equipped models — including the Urbia Green, Mira C Green, Serelia Green, and Niagara Green — show 116 instead.
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
- Faulty or seized circulation pump on the underfloor circuit Common
The circulation pump is responsible for keeping water moving around the underfloor loops. If it has seized — which is especially common after a long summer lay-off — hot water stagnates and heat builds up rapidly until the safety thermostat trips. Listening for pump noise and feeling for vibration through its casing can give a first indication of whether it is running.
- Flow temperature set too high for underfloor heating Common
Underfloor heating circuits should operate at a much lower temperature than a standard radiator circuit — typically no more than 45–50°C. If a thermostatic blending valve is absent or incorrectly set, full-temperature boiler water can reach the underfloor loops, quickly pushing past the safety thermostat's trip point.
- Sludge or debris restricting circulation Sometimes
A build-up of magnetite sludge or scale in the underfloor pipework reduces flow rate, causing localised hot spots. This can also show up as cold patches in the floor, noisy pipework, or other zones of the heating system underperforming at the same time.
- Faulty flow temperature sensor Sometimes
If the boiler's heating flow probe is giving inaccurate readings, the boiler may allow water to heat beyond its intended target without realising. Comparing the temperature displayed on the boiler against an independent measurement of the pipe surface can reveal a significant discrepancy pointing to a defective sensor.
- Defective or wiring fault at the underfloor safety thermostat itself Rare
Occasionally the thermostat unit itself develops a fault, or a loose or corroded connection at its terminals gives a false open-circuit signal even when the floor temperature is normal. This is worth investigating once genuine overheating has been ruled out.
How to fix it
- Locate and manually reset the underfloor heating safety thermostat DIY safe
The manual-reset thermostat is normally situated on or near the underfloor heating manifold or its control enclosure — look for a small button, often red or white, that can be pressed in with a finger or a fine tool. The boiler will not restart until this is done. Before pressing it, allow a few minutes for the system to cool down.
- Reset the boiler once DIY safe
After resetting the floor thermostat, press the boiler's reset button once and observe whether it fires up and stays running. If the fault reappears promptly, do not continue resetting — repeated lockouts without addressing the root cause will not resolve the problem and may mask a worsening issue.
- Check that the underfloor heating pump is running DIY safe
With the heating on, place a hand on the pump body and listen for a faint hum or feel for vibration. Complete silence and no warmth suggest the pump is not spinning. After a long summer shutdown, pumps can seize due to limescale on the rotor shaft — an engineer can free the rotor using the manual bleed screw on the pump head.
- Verify the underfloor circuit flow temperature setting DIY safe
Check the boiler's controls or the blending valve setting to confirm the underfloor circuit is being supplied with water no hotter than 45–50°C. If your installation mixes underfloor and radiator circuits from the same boiler without a dedicated blending valve, inform the engineer — fitting one may be needed.
- Inspect the system for signs of sludge or poor circulation DIY safe
Cold patches in the floor, gurgling sounds from pipework, or other heating zones also underperforming can all point to a circulation blockage. Note these symptoms before calling an engineer — the information will help them diagnose quickly.
- Call a Gas Safe registered engineer to investigate and carry out repairs Gas Safe engineer
Any work on the boiler's internal components — including the flow sensor, pump replacement, blending valve installation, or PCB — must be carried out by a Gas Safe registered engineer. They can also test the underfloor thermostat for continuity, check sensor accuracy, and arrange a power flush if sludge is identified. Always ask to see their Gas Safe ID card before work begins.
Parts you may need
- Underfloor heating manual-reset safety thermostat · from £35
- Underfloor heating circulation pump · from £120
- Thermostatic blending valve (for underfloor circuit) · from £75
- Heating flow temperature sensor · from £25
- Pump head seal / pump service kit · from £20
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 £100–£350, depending on the underlying cause.
Frequently asked questions
Why won't my Chaffoteaux boiler restart even after pressing the reset button?
Fault code 116 uses a manual-reset safety thermostat on the underfloor heating manifold — this is separate from the boiler's own reset button. You need to physically press the reset button on the thermostat unit itself (usually located at the manifold or its control box) before the boiler's reset will work. If the boiler still locks out again shortly after, there is an underlying issue — most likely a pump fault or excessive flow temperature — that needs a Gas Safe engineer to diagnose and fix.
Is Chaffoteaux fault code 116 the same as error E30?
Yes, they describe the same condition. E30 is the alphanumeric code shown on older Chaffoteaux & Maury boilers that have a simpler display, while 116 is the numeric equivalent displayed on newer models such as the Urbia Green, Mira C Green, Serelia Green, and Niagara Green. Both indicate that the underfloor heating circuit's safety thermostat has tripped open due to overheating.
How much does it cost to fix a Chaffoteaux 116 fault in the UK?
Most people with this fault pay somewhere between £100 and £350. A straightforward thermostat reset plus investigation by an engineer typically costs £100–£180 including callout. If the circulation pump needs replacing, expect £200–£350 in parts and labour combined. A power flush to clear sludge from the underfloor circuit can add £300–£500 on top if blockage is found to be the root cause — though that is less common. Major boiler-side components such as a PCB, if found to be involved, can push costs higher, but that would be unusual for this specific fault.
Can I prevent fault code 116 from coming back every autumn when I switch the heating on?
Yes — seasonal maintenance goes a long way. Before switching your heating on after a long summer break, check that the underfloor heating pump spins freely (an engineer can manually free a seized rotor), bleed any air from the underfloor loops, and confirm the blending valve or temperature settings are still correct. Having the system serviced annually by a Gas Safe engineer keeps all these components in check and catches deteriorating parts before they trigger a safety shutdown.