Chaffoteaux 713 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 713 fault code mean?
Fault code 713 appears on Chaffoteaux multizone system boilers (such as the Talia, Niagara, and Inoa) when the control board detects an abnormal or absent signal from the NTC temperature sensor fitted to the return pipe of heating Zone 3. This sensor — a Negative Temperature Coefficient (NTC) thermistor — continuously monitors the temperature of water flowing back into the boiler from Zone 3. Its resistance drops as the water warms up, and the PCB uses those readings to modulate the burner and prevent overheating. When the signal falls outside the expected range or disappears entirely, the boiler logs code 713 and may lock out. For context, this code sits within a broader family of multizone probe errors: codes 701–703 relate to flow probe anomalies on Zones 1–3, code 712 flags an issue with the Zone 2 return probe, and code 713 targets the Zone 3 return probe specifically. Note: this code applies to multizone models with an Expert Control-style interface. Older single-zone Chaffoteaux boilers such as the Britony Combi SE use a completely different LED-based fault system and will not display a 713 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
- Faulty or failed Zone 3 return NTC sensor Common
The thermistor itself has degraded over time or failed outright. A failed sensor will produce a reading that is either completely absent or far outside the expected resistance range, causing the PCB to log the fault immediately.
- Loose, corroded, or damaged wiring or connector Common
The electrical connection between the Zone 3 return sensor and the PCB can deteriorate due to vibration, heat cycling, or age. Even a partially broken connection is enough to send an erratic signal that triggers the fault.
- Moisture on the sensor or PCB connector Sometimes
Condensation or a minor water leak near the sensor connector can alter the resistance reading. This is particularly common in boiler cupboards with poor ventilation or where a nearby pipe joint has been weeping.
- Short circuit in the sensor circuit Sometimes
A short within the sensor wiring circuit — or coolant temperatures running above the recommended range — can damage the sensor circuit and register a false or out-of-bounds reading on the PCB.
- Incorrect zone wiring or configuration Rare
If the system has been recently installed, extended, or had zone valves or wiring modified, incorrect connection of the Zone 3 return sensor can produce this code. Worth checking if the fault appeared immediately after any system work.
- PCB fault Rare
If the sensor and all wiring check out correctly, the PCB itself may have lost the ability to read the sensor input accurately. This is the least common cause but must be investigated if sensor replacement does not clear the fault.
How to fix it
- Attempt a single boiler reset DIY safe
Locate the reset button on your Chaffoteaux boiler, press it once, and wait to see whether the boiler fires up normally. If the 713 code returns within a short time, do not keep resetting — repeated resets without resolving the underlying fault can mask the problem and potentially cause further damage. Move on and call an engineer.
- Check for any obvious external causes such as a water leak near the Zone 3 sensor area DIY safe
If you can safely access the boiler without removing any panels, look for signs of dripping water or condensation around the Zone 3 pipework. A weeping joint near the sensor could introduce moisture that disrupts the reading. Do not touch any internal components — simply note what you see and report it to your engineer.
- Have a Gas Safe engineer inspect the Zone 3 return sensor wiring and connector Gas Safe engineer
The engineer should trace the wiring harness from the Zone 3 return sensor back to the PCB, checking for loose terminals, corrosion, heat damage, or any break in the cable. Connectors should be unplugged, inspected, cleaned if necessary, and reseated securely. This step alone resolves a significant number of 713 faults.
- Test the NTC sensor electrically Gas Safe engineer
Using a multimeter, the engineer will measure the sensor's resistance at a known water temperature and compare it against the manufacturer's specification for that sensor type. A reading that is open-circuit, short-circuit, or significantly out of range confirms a faulty sensor. The pipe contact surface should also be clean and free of corrosion before any new sensor is fitted.
- Replace the Zone 3 return NTC sensor if confirmed faulty Gas Safe engineer
NTC return sensors clip onto the outside of the pipe rather than being immersed in the water circuit, so the system does not typically need to be drained for this replacement. The engineer will fit a new sensor — ideally a genuine Chaffoteaux or approved equivalent part — and may apply a small amount of heat-conductive compound between the sensor body and the pipe to ensure good thermal contact. The boiler should then be reset and tested across all zones.
- Arrange PCB investigation or replacement if the fault persists Gas Safe engineer
If a new sensor and confirmed-good wiring do not clear the 713 code, the PCB's ability to read the sensor input must be assessed. PCB replacement is a significant cost, so a competent engineer will thoroughly re-check the circuit before recommending it. Bear in mind that on older Chaffoteaux boilers, the cost of a PCB replacement may make a new boiler more economical — ask your engineer for an honest assessment.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
All internal boiler diagnostics and repairs on a Chaffoteaux multizone system must be carried out by a Gas Safe registered engineer. You can verify any engineer's registration at gassaferegister.co.uk. Do not allow unregistered individuals to work on your boiler — it is illegal under the Gas Safety (Installation and Use) Regulations 1998 and risks carbon monoxide exposure.
Parts you may need
- Zone 3 return NTC temperature sensor (thermistor) · from £20
- Sensor wiring harness / connector · from £25
- PCB (main control board) · from £350
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–£300, depending on the underlying cause.
Frequently asked questions
Is fault code 713 dangerous — will my boiler explode or leak carbon monoxide?
Code 713 is a sensor monitoring fault rather than a direct safety lockout caused by overheating or a combustion problem, so the immediate risk level is lower than codes such as an overheat or flame-failure error. That said, the sensor circuit exists partly to prevent the system from running outside safe temperature limits, so you should not ignore it or continue resetting indefinitely. Get it diagnosed promptly by a Gas Safe engineer.
Can I fix Chaffoteaux fault 713 myself?
Resetting the boiler once is the only step a homeowner should take. Everything beyond that — checking wiring, testing the sensor, replacing components — requires a Gas Safe registered engineer. NTC sensors are inexpensive parts, but accessing them inside the boiler casing and verifying the electrical circuit safely is not a DIY job.
How much does it cost to fix a Chaffoteaux 713 fault code in the UK?
Most people with a 713 fault pay somewhere between £100 and £300 all-in, depending on what the engineer finds. A wiring or connector fix at the lower end, and a sensor replacement with a standard callout fee at the higher end, typically fall within that range. If the PCB turns out to be at fault, the bill can rise to £350–£550 or more including parts and labour — at that point it is worth asking your engineer whether repair or replacement makes more financial sense, particularly on a boiler over ten years old.
My Chaffoteaux boiler is showing a similar code — 712 or 701 to 703 — is that the same fault?
Not quite. Codes 701, 702, and 703 relate to flow probe anomalies on Zones 1, 2, and 3 respectively, while codes 712 and 713 relate to return probe anomalies on Zones 2 and 3. The root causes and diagnostic approach are very similar — faulty NTC sensor, wiring issue, or PCB — but the affected sensor and its location on the pipework will differ. Mention the exact code to your engineer so they check the correct sensor from the outset.
My Chaffoteaux boiler is quite old — is it worth repairing a 713 fault?
Chaffoteaux boilers generally last between 10 and 15 years with regular servicing. If yours is approaching or past that age and the 713 fault turns out to require a PCB replacement (the most expensive scenario), the repair cost relative to the remaining lifespan of the boiler may not represent good value. A straightforward sensor or wiring fix on a well-maintained boiler is almost always worth doing. Ask your Gas Safe engineer for an honest appraisal before committing. Also note that Chaffoteaux is now part of the Ariston Group, so parts availability for older models should be confirmed before agreeing to any repair.