Chaffoteaux 1P6 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 1P6 fault code mean?
The 1P6 fault code on a Chaffoteaux boiler indicates a Flow Check Failed lockout. The '1' prefix identifies this as a hydraulic circuit fault — the boiler monitors water movement through the primary heating circuit and, when it cannot confirm adequate circulation, it shuts itself down as a safety measure. The 'P' designation confirms this is a protection lockout rather than a simple warning. In plain terms, the boiler has detected that water is not flowing around the system as it should be, and has refused to fire until the underlying problem is addressed. This code sits within the 1P family of hydraulic protection faults on Chaffoteaux boilers, which all relate to circulation and flow issues in the primary circuit.
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
- Low system pressure or air trapped in the circuit Common
If the boiler pressure has dropped below around 1 bar, or air has become trapped in the primary circuit, water cannot circulate freely. This is the most frequent trigger for the 1P6 lockout and is worth checking first. The pressure gauge on the front of the boiler should read between 1.0 and 1.5 bar when the system is cold.
- Circulation pump failure or seizure Common
A pump that has seized, is partially blocked, or is nearing the end of its service life will fail to move water sufficiently even when system pressure is correct. A tell-tale sign is a very hot flow pipe alongside a cold return — the heat is not being distributed around the circuit. You may also notice unusual silence, humming, or stuttering from the pump housing.
- Sludge, scale, or debris restricting flow Sometimes
Over time, magnetite sludge and limescale can build up inside the heat exchanger and pipework, reducing water flow to the point where the boiler's flow-check routine fails. A flow sensor that has become stuck due to debris accumulation can also trigger the same lockout. Older systems or those without a magnetic filter are particularly susceptible.
- Faulty NTC temperature sensor or wiring fault Sometimes
The boiler uses NTC thermistor probes on both the flow and return pipes to infer whether circulation is taking place. If one of these sensors has drifted out of calibration, developed a wiring fault, or failed entirely, the boiler may incorrectly conclude that water is not moving even when the pump is working correctly.
- PCB fault Rare
The PCB acts as the control centre, processing signals from the pump and temperature sensors. A fault on the board — whether due to a failed component, moisture ingress, or a power surge — can prevent it from confirming that the circulation pump is operating, triggering a precautionary lockout. This is the least common cause but should be considered once all other components have been ruled out.
How to fix it
- Check the system pressure gauge DIY safe
Look at the pressure gauge on the boiler fascia. It should read between 1.0 and 1.5 bar when the system is cold. If it reads below 1 bar, use the filling loop to top up the pressure to around 1.2 bar. Refer to your boiler manual for the location of the filling loop — typically two small valves under the boiler connected by a braided hose.
- Bleed any trapped air from your radiators DIY safe
Trapped air prevents water from circulating freely. Starting with the radiator furthest from the boiler, use a radiator bleed key to open the bleed valve slightly until water (not air) trickles out, then close it. Work your way back towards the boiler. After bleeding, recheck the system pressure and top up if needed.
- Ensure all radiator valves and isolation valves are fully open DIY safe
Closed thermostatic radiator valves or isolation valves on the pipework can restrict flow enough to trigger the lockout. Check that every radiator valve is open and that no isolation valves beneath the boiler are partially closed.
- Reset the boiler once and observe DIY safe
Press the reset button on the boiler's front panel and wait at least 60 seconds to see whether the boiler fires and runs normally. If it locks out again within a short time, do not keep resetting — repeated resets without resolving the underlying fault can mask the problem or cause further damage. Note whether the lockout returns immediately or after the boiler has been running for a few minutes, as this information will help the engineer diagnose the fault.
- Have a Gas Safe engineer inspect and test the circulation pump Gas Safe engineer
If basic checks have not resolved the issue, a registered engineer should test the pump electrically and physically. They will check whether the impeller is spinning freely, measure current draw, and look for signs of seizure or blockage in the pump body and return filter. A stuck pump impeller can sometimes be freed without a full replacement, saving cost.
- Consider a power flush if sludge is suspected Gas Safe engineer
If the system has not been flushed in several years, or if you have cold spots on radiators or noisy pipework alongside the 1P6 fault, a power flush carried out by a heating engineer can clear accumulated magnetite and debris. Installing a magnetic system filter afterwards helps prevent recurrence.
- Have the NTC temperature sensors and associated wiring tested Gas Safe engineer
A Gas Safe engineer will use a multimeter to test the resistance of the flow and return NTC sensors at various temperatures, comparing readings against the manufacturer's specification. Damaged wiring or corroded connectors between the sensors and PCB can produce the same symptoms as a failed sensor itself.
- If all else fails, have the PCB assessed for replacement Gas Safe engineer
Should the pump, sensors, wiring, and hydraulic system all test correctly yet the 1P6 fault persists, the PCB is the likely culprit. PCB diagnosis and replacement must be carried out by a qualified engineer. Note that PCB replacement is relatively expensive, so confirm diagnosis thoroughly before committing to this repair.
- Call a Gas Safe registered engineer Gas Safe engineer
If the fault has not cleared after checking pressure, bleeding radiators, and a single reset, contact a Gas Safe registered engineer to carry out a full diagnosis. You can verify any engineer's credentials at gassaferegister.co.uk. Do not attempt to dismantle the pump, sensors, or PCB yourself.
Parts you may need
- Circulation pump (replacement) · from £120
- NTC flow/return temperature sensor · from £25
- Magnetic system filter · from £55
- PCB (printed circuit board) · from £220
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 the Chaffoteaux 1P6 fault myself?
There are a few safe checks you can carry out yourself: verifying and topping up system pressure via the filling loop, bleeding trapped air from radiators, ensuring all valves are open, and performing a single reset. However, if the lockout returns after these steps, the fault is likely with the pump, a sensor, or the PCB — all of which require a Gas Safe registered engineer to diagnose and repair safely.
How much does it cost to fix a Chaffoteaux 1P6 fault?
Most people with this fault end up paying between £120 and £380, depending on what is found. A stuck or worn circulation pump — including labour — typically costs £150–£300. Replacing an NTC temperature sensor usually comes to around £100–£180 all in. A power flush, if sludge is the underlying cause, generally runs £300–£500. PCB replacement is the most expensive outcome at £350–£600 or more, but it is also the least common cause. Emergency call-outs outside normal hours will add a premium of roughly £100–£200 on top.
Why does my Chaffoteaux keep showing 1P6 after I reset it?
If the lockout returns quickly after each reset, it means the root cause — most often a failing circulation pump, very low pressure, or heavy sludge build-up — has not been resolved. Repeatedly resetting without fixing the underlying fault can sometimes cause further wear on components. Limit yourself to one or two resets after checking pressure and bleeding radiators, then call an engineer.
Is the 1P6 code related to other Chaffoteaux flow fault codes like 1P3 or 1P7?
Yes. The '1' prefix on Chaffoteaux fault codes identifies the hydraulic circuit functional unit, and the full 1P family of codes all relate to flow and circulation protection lockouts. Codes such as 1P3 through 1P7 share the same underlying causes — insufficient water flow, pressure issues, pump problems, sludge, or sensor faults — and are investigated and repaired in broadly the same way. If your display shows a code that looks slightly different, cross-reference it with your model's manual, as the 7-segment display on some Chaffoteaux models can make certain digits look similar to letters.