Chaffoteaux 1P4 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 1P4 fault code mean?
The 1P4 fault code (also shown as F1P4 or sometimes referenced as fault 108 on certain Chaffoteaux models) indicates that the water pressure in the primary heating circuit has fallen below the minimum threshold the boiler needs to operate safely. When pressure drops to this level, the boiler will stop firing and display 1P4 to protect itself and the system from damage. In many cases this is a straightforward fix — repressurising via the filling loop — but if the fault keeps returning, something else is causing the pressure to escape and a Gas Safe engineer will need to investigate.
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
- System pressure naturally dropping over time Common
All sealed central heating systems lose a small amount of pressure gradually, particularly after bleeding radiators or following a period of heavy use. If the gauge has crept below 1.0 bar, this is the most likely explanation and repressurising should resolve it immediately.
- Leak somewhere in the system Common
A slow weep from a radiator valve, pipework joint, or boiler component can bleed pressure away over days or weeks. If you find yourself topping up the system repeatedly — say every few days — a leak is the probable culprit. Check radiators, visible pipework, and the area beneath the boiler for damp patches or staining.
- Faulty or waterlogged expansion vessel Sometimes
The expansion vessel absorbs pressure changes as water heats and cools. Over time its internal membrane can fail, causing pressure to drop repeatedly or fluctuate erratically. A failed expansion vessel cannot be repaired and must be replaced by an engineer.
- Weeping pressure relief valve (PRV) Sometimes
The PRV is designed to release water if pressure gets dangerously high, but the valve seat can wear and allow a slow, continuous drip to waste. If there is a damp patch or discharge near the overflow pipe outside, this is worth checking. PRV replacement requires an engineer.
- Faulty pressure sensor or transducer Rare
Occasionally the sensor that monitors circuit pressure gives an inaccurate reading, triggering a 1P4 fault even when the actual system pressure is adequate. This is less common but should be considered if the pressure gauge looks fine yet the fault persists after repressurising.
How to fix it
- Check the pressure gauge reading DIY safe
Find the pressure gauge — usually on the front panel or underneath the boiler. If it reads below 1.0 bar, low pressure is almost certainly the cause of the 1P4 fault. If it reads above 1.0 bar, the issue may be a faulty pressure sensor rather than actual low pressure, in which case skip to calling an engineer.
- Repressurise the system using the filling loop DIY safe
Locate the filling loop beneath the boiler — it is usually a short, silver braided hose with two small valve handles. Slowly open both valves to allow mains water into the circuit. Watch the gauge carefully and close both valves as soon as the needle reaches 1.2–1.5 bar. Do not overfill. If your boiler has a keyless filling link or a different design, follow the specific instructions in your Chaffoteaux manual for that model.
- Reset the boiler DIY safe
Once the pressure is restored, press and hold the reset button on the control panel (usually marked with a flame symbol or the word Reset) for a few seconds until the boiler attempts to restart. The 1P4 code should clear. If it does not clear, or if the boiler loses pressure again within a day or two, move on to the steps below.
- Inspect radiators and visible pipework for leaks DIY safe
Walk around the property and feel along radiator valves, check the floor beneath each radiator, and look at any exposed pipework for damp, rust staining, or white limescale deposits — all signs of a slow weep. Do not attempt to repair any leaks yourself; just note the location to pass on to an engineer.
- Check the condensate pipe is not frozen (winter months only) DIY safe
Although a frozen condensate pipe usually triggers a different fault code, a blockage can sometimes cause unusual system behaviour. If the white plastic pipe that exits the boiler to an outside drain feels solid in cold weather, you can carefully thaw it using warm (not boiling) water poured over the exterior section.
- Call a Gas Safe registered engineer Gas Safe engineer
If the 1P4 code returns after repressurising, if you cannot locate or stop the source of pressure loss, or if you suspect the expansion vessel, pressure relief valve, or pressure sensor is at fault, contact a Gas Safe registered engineer. Continuing to top up the system without addressing the root cause can mask a more serious problem and may invalidate your boiler warranty.
Parts you may need
- Expansion vessel (replacement) · from £80
- Pressure relief valve (PRV) · from £25
- Pressure sensor / transducer · from £35
- Filling loop assembly · 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 £120–£350, depending on the underlying cause.
Frequently asked questions
Can I fix the Chaffoteaux 1P4 fault myself?
Yes, in many cases. If the pressure gauge reads below 1.0 bar, repressurising the system via the filling loop and then resetting the boiler is a DIY-safe task. If the fault clears and the pressure stays stable, no engineer is needed. However, if the pressure drops again within a few days, or you can see a leak, you should call a Gas Safe registered engineer to investigate rather than keep topping it up.
Why does my Chaffoteaux boiler keep losing pressure and showing 1P4?
Recurring pressure loss almost always points to one of three things: a slow leak on a radiator, valve, or joint somewhere in the system; a waterlogged expansion vessel that can no longer absorb pressure changes; or a weeping pressure relief valve allowing water to drip to waste. A Gas Safe engineer can diagnose which of these is causing the problem — topping up repeatedly without fixing the root cause is not a long-term solution and can cause further damage.
How much does it cost to fix a Chaffoteaux 1P4 fault in the UK?
If you can resolve it by repressurising yourself, the cost is nothing. If an engineer is needed, most people pay between £120 and £350 all-in, depending on the cause. Expansion vessel recharge or replacement typically falls in the £120–£280 range, and a pressure relief valve swap is usually £120–£200 including labour. Leak detection and repair can push costs higher depending on where the leak is. Note that very complex repairs such as a PCB or heat exchanger failure can cost considerably more, but those are unlikely to be the cause of a 1P4 fault specifically.
Is 1P4 the same as fault code 108 on Chaffoteaux boilers?
Yes — some Chaffoteaux models display the same underlying low-pressure fault as F1P4, 1P4, or fault 108 depending on the model and firmware version. All three refer to the primary circuit pressure falling below the safe operating threshold, and the diagnosis and fix are the same in each case: check the gauge, repressurise to 1.2–1.5 bar, and reset. If the fault returns, call a Gas Safe engineer.