What the PH Fault Means on Your Ideal Boiler
PH on a boiler display stands for pump/pre-heat run-on — the boiler is telling you the circulating pump is running while the burner is off. On Ideal Logic, Logic+, Vogue and Independent models the PH code appears at the end of a heating or hot water demand while the pump dissipates residual heat from the heat exchanger, and it should clear on its own within a few minutes.
So when homeowners ask what PH means on a boiler, the short answer is: it is normally a status code, not a fault. It only becomes a problem when PH stays on the display permanently, when the boiler will not fire while showing PH, or when it appears alongside low pressure or overheat symptoms.
Ideal Boiler PH Fault Code Causes
Why PH sticks on the display
- Pump overrun continuing because the boiler cannot shed heat — often a blocked heat exchanger or sludged system.
- Failed or seized circulating pump so the flow sensor never sees the temperature drop it expects.
- Faulty flow or return thermistor giving the PCB an incorrect temperature reading.
- Air locked primary circuit preventing proper circulation during the overrun period.
- Closed or partially closed isolation valve after recent radiator or valve work.
- System pressure sitting below 1 bar, which restricts flow and extends the overrun.
- PCB fault where the run-on timer does not reset correctly.
How To Fix The PH Code On An Ideal Boiler
Step-by-step checks
- Wait five minutes — a normal PH run-on clears on its own once the heat exchanger cools.
- Check the pressure gauge cold; re-pressurise to between 1.0 and 1.5 bar using the filling loop if it is low.
- Make sure all radiator and isolation valves are fully open and bleed any radiators that are cold at the top.
- Turn the boiler off at the fused spur for 60 seconds, then back on, and run a fresh heating demand.
- If PH remains on the screen permanently, or the boiler will not fire, book a Gas Safe registered engineer — the pump, thermistors or heat exchanger need testing.
When To Call A Gas Safe Engineer
Call an engineer if PH is displayed constantly, if radiators stay cold while the pump is audibly running, if the boiler kettles or bangs, or if the code is accompanied by repeated pressure loss. Our engineers carry Ideal pumps, thermistors and PCBs and cover London and the M25 24 hours a day, with commercial work charged from £75+VAT per half hour and domestic from £60+VAT per half hour.
Common Ideal Boiler Codes
| Code | Meaning | Typical fix |
|---|---|---|
| PH | Pump overrun / heat dissipation in progress | Normally clears in minutes; if permanent check pump, thermistors and flow. |
| F1 | Low water pressure | Re-pressurise to 1.0–1.5 bar and check for leaks. |
| F2 | Flame loss / no flame detected | Check gas supply, gas valve and flame electrode. |
| L2 | Ignition lockout | Reset once; if repeated, electrode or gas valve testing needed. |
| F3 | Fan fault | Fan, harness or PCB fan drive requires testing. |
| L6 | Flow thermistor fault | Replace flow thermistor / check wiring. |
PH Fault Code FAQs
What does PH mean on a boiler?
PH means pump overrun (pump/heat dissipation). The circulating pump keeps running after the burner switches off to remove residual heat from the heat exchanger. On an Ideal boiler it is a normal status code and usually clears within a few minutes.
Is the PH code on an Ideal boiler a fault?
Not usually. It only indicates a fault if PH stays on the display permanently, the boiler will not fire while showing PH, or it appears with low pressure, kettling or overheating symptoms.
How do I clear the PH code?
Allow the overrun to finish, check the pressure is 1.0–1.5 bar, open all valves, bleed the radiators and cycle the power. If PH persists, the pump, thermistors or heat exchanger need engineer diagnosis.
How much does it cost to fix a PH fault?
Domestic diagnostics start from £60+VAT per half hour with a minimum one-hour charge; commercial from £75+VAT per half hour. Parts such as a pump or thermistor are quoted before any work goes ahead.
Need this fault fixed?
Our Gas Safe registered engineers diagnose and repair this fault across London and the M25. Book a boiler repair, arrange a boiler service, or call us out for commercial boiler repair. Call 0208 935 5572.
