Chaffoteaux 1P8 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 1P8 fault code mean?
If your Chaffoteaux boiler is showing '1P8', this is almost certainly not a genuine fault code — it is a display misread. On segmented digital displays fitted to many Chaffoteaux models, the digit '0' can render in a way that closely resembles the letter 'P', causing homeowners to read '108' as '1P8'. Code 108 is a confirmed and well-documented Chaffoteaux fault meaning the system water pressure has fallen below the safe minimum threshold. Most Chaffoteaux boilers need to sit between 1.0 and 1.5 bar when cold to operate correctly. Once pressure drops beneath that level, the boiler locks out and displays 108 (which you may be seeing as 1P8) to protect the heat exchanger and pump from running dry.
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
- Recently bled radiators Common
Bleeding a radiator releases trapped air from the system, but it also lets a small amount of water out at the same time. Even bleeding just one or two radiators can be enough to nudge system pressure below the 1.0 bar threshold and trigger code 108. This is the most common reason this fault appears, and it is the easiest to fix.
- Gradual natural pressure loss Common
Central heating systems lose a very small amount of pressure over time through micro-seepage at fittings and valve glands. A slow drift from 1.5 bar to below 1.0 bar over several months, with no obvious leak visible, is entirely normal and simply requires the system to be topped up via the filling loop.
- Leaking or weeping pressure relief valve (PRV) Sometimes
The PRV is a safety device designed to open if pressure climbs too high. If the valve seat becomes worn or scaled, it can weep constantly, allowing water to drip steadily through the orange or copper discharge pipe that exits through an outside wall. Each time the boiler heats up, a little water is lost. If you see drips outside your property near the boiler flue area, this is a strong indicator.
- Failing expansion vessel Sometimes
The expansion vessel contains a rubber diaphragm that separates a pressurised air charge from the system water. As the diaphragm ages, the air charge can be lost, meaning the vessel can no longer absorb the volume changes that occur when water heats and cools. Pressure then becomes unstable — sometimes spiking and causing the PRV to lift, sometimes dropping low enough to trigger code 108. A failed expansion vessel requires attention from a Gas Safe engineer.
- Internal boiler leak Rare
A slow drip from a heat exchanger joint, diverter valve O-ring, or pump seal inside the boiler casing will cause steady pressure loss with no visible external sign of water. If you are topping up the system more than once every few weeks and can find no external leak, an internal source should be investigated by an engineer.
How to fix it
- Check the pressure gauge DIY safe
Locate the pressure gauge on your Chaffoteaux boiler — it is usually visible on the front fascia or just beneath the boiler casing. If the needle or digital reading is below 1.0 bar, low pressure is confirmed as the cause of the 1P8 / 108 fault. If the gauge already reads 1.0 bar or above, do not add more water; contact an engineer to investigate further.
- Repressurise using the filling loop DIY safe
Find the filling loop — a short, silver braided hose with one or two small lever or key-operated valves, typically located underneath the boiler. Before opening anything, ensure the boiler is switched off and has cooled down. Slowly open the filling loop valve(s) and watch the pressure gauge rise. Stop when the reading reaches 1.2–1.5 bar. Close the valve(s) fully. Never exceed 1.5 bar when cold, as overpressure can cause the PRV to release water.
- Reset the boiler DIY safe
Once pressure is restored to the correct level, press and hold the reset button on the control panel (typically marked with a flame or reset symbol) for around three seconds, or until the boiler attempts to fire. Allow the boiler to complete a full heating cycle and confirm the fault code has cleared. Do not reset more than two or three times without addressing the root cause.
- Check for obvious external leaks DIY safe
Walk around the boiler and any visible pipework, radiators, and towel rails. Look for damp patches, water stains, or corrosion on pipe joints and radiator valves. Also look outside your property for the boiler's discharge pipe (usually a copper or orange plastic pipe exiting through the wall near the boiler) — a steady drip from this pipe indicates the PRV may be weeping. Note anything you find and report it to your engineer.
- Call a Gas Safe registered engineer if pressure drops again or a leak is found Gas Safe engineer
If the pressure falls below 1.0 bar again within a few weeks, or if you have found a leak or a dripping PRV discharge pipe, do not simply keep topping up. Repeated repressurisation without fixing the root cause can waterlog the expansion vessel and cause further problems. A Gas Safe engineer should inspect the system, recharge or replace the expansion vessel if needed, replace a faulty PRV, or trace and repair any internal or external leak.
Parts you may need
- Pressure relief valve (PRV) · from £25
- Expansion vessel (replacement) · from £60
- Filling loop assembly · from £20
- Pressure gauge · from £15
- Pump seal kit · from £18
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
Is 1P8 a real Chaffoteaux fault code or am I misreading the display?
Almost certainly a misread. Chaffoteaux boilers use segmented digital displays on which the digit '0' can look like the letter 'P', especially on older or faded screens. The genuine fault code is 108, which is the confirmed low water pressure fault. You will not find '1P8' in any Chaffoteaux manual because it does not exist as a standalone code — treat it as 108 and follow the low pressure advice on this page.
How often should I need to top up my Chaffoteaux boiler pressure?
A healthy system should not need topping up more than once or twice a year, if that. If you find yourself adding water every few weeks or every month, something is causing an abnormal pressure loss. Common culprits are a weeping PRV, a failing expansion vessel diaphragm, or a slow leak somewhere on the system. Continually repressurising without fixing the root cause can eventually waterlog the expansion vessel and make the problem worse. Book a Gas Safe engineer to investigate.
Can I repressurise my Chaffoteaux boiler myself?
Yes, topping up the system pressure via the filling loop is one of the few boiler-related tasks that is safe for a homeowner to carry out, provided you follow the process carefully. Switch the boiler off first, open the filling loop valve slowly, watch the gauge, and stop at 1.2–1.5 bar. Do not overfill. If you are unsure where the filling loop is or the boiler has an integral filling key rather than a visible loop, consult your model's user guide or call an engineer.
Could the expansion vessel failure cost more than the figures quoted?
For most Chaffoteaux models the expansion vessel replacement sits comfortably within the £180–£350 range including parts and labour. However, on some older or combi models where the vessel is awkwardly positioned or where the boiler must be substantially stripped down to access it, costs can rise to £450 or more. If the boiler is over 10–12 years old and the engineer also finds other wear items, it may be worth discussing whether a full boiler replacement makes better financial sense than investing in multiple repairs.