Protherm F.07 Fault Code: Causes, Fixes & Repair Costs
What does the Protherm F.07 fault code mean?
The F.07 code appears on Protherm boilers when the flame monitoring system detects a problem confirming that a flame is present and stable. When the boiler attempts to fire, the ignition electrode produces a spark to light the burner. A separate ionisation (flame-sensing) electrode then checks that combustion is actually taking place and sends a signal back to the PCB. If that signal is absent, too weak, or inconsistent, the boiler shuts off the gas supply as a safety measure and displays F.07. On the Protherm display, the letter F flashes alongside the error number. The fault can stem from a gas supply interruption, a degraded or dirty ionisation electrode, or a fault within the main control board that prevents it from correctly reading the flame signal. The boiler also stores the ten most recent fault codes, so an engineer can review whether F.07 has been appearing repeatedly or as a one-off event.
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
- Gas supply interruption Common
If the gas supply to the boiler is disrupted — whether because the isolation valve has been turned off, there is a local supply issue, or a prepayment meter has run out of credit — the burner cannot establish or sustain a flame. The ionisation electrode never receives a signal, and F.07 is triggered. Checking that other gas appliances in the property are working normally is the simplest first step.
- Dirty or worn ionisation electrode Common
The ionisation electrode sits inside the combustion chamber and is exposed to high temperatures and combustion gases every time the boiler fires. Over time, carbon deposits, soot, or corrosion build up on the electrode tip, reducing the strength of the electrical signal it passes back to the PCB. If the signal falls below the threshold the PCB expects, the boiler interprets this as no flame being present, even when combustion is occurring. Electrodes typically need attention every three to five years depending on usage intensity.
- Damaged electrode lead or wiring fault Sometimes
The low-voltage signal from the ionisation electrode travels back to the PCB via a dedicated lead. If this lead has cracked insulation, a loose connector, or a short circuit caused by proximity to hot components, the signal can drop out intermittently or altogether. The electrode itself may be perfectly serviceable while the wiring is the actual culprit.
- Faulty gas valve Sometimes
If the gas valve fails to open fully — or opens with an incorrect flow rate — the burner flame may be too weak or unstable for the ionisation electrode to register reliably. The PCB then closes the valve and logs F.07. Gas valve faults can also develop after voltage surges on the mains supply, which Protherm boilers can be sensitive to.
- Faulty PCB (main control board) Rare
The PCB is responsible for initiating the ignition sequence, reading the signal from the ionisation electrode, and deciding whether combustion has been established. If the PCB itself has developed a fault — whether from component degradation, a power surge, or moisture ingress — it may fail to process a perfectly good flame signal correctly. PCB failure tends to be a diagnosis of exclusion, arrived at after the electrode, wiring, and gas supply have been ruled out.
How to fix it
- Check that your gas supply is working DIY safe
Turn on a gas hob or check another gas appliance in your home. If nothing is working, the issue is likely a supply interruption rather than a boiler fault. Contact your gas supplier or check whether a prepayment meter needs topping up. Also confirm that the boiler's isolation valve (usually on the pipework immediately below or beside the boiler) is in the open position — handle in line with the pipe means open.
- Reset the boiler once or twice DIY safe
If the gas supply is confirmed as normal, press and hold the reset button on the boiler for a few seconds until the display clears and the unit attempts to restart. Give it a full ignition cycle before deciding whether the fault has cleared. Only reset two or three times at most — repeated resets without the fault resolving will not fix an underlying problem and may mask useful diagnostic information for an engineer.
- Arrange a Gas Safe engineer inspection of the ionisation electrode and leads Gas Safe engineer
A registered engineer will safely access the combustion chamber, inspect the ionisation electrode for carbon deposits, cracking, or damage to the ceramic body, and check the condition of the connecting lead and its connectors. If the electrode is simply sooted up, careful cleaning may restore normal operation. If it is physically degraded or the lead is damaged, the affected parts will need to be replaced. This is the most common resolution for F.07 and generally the most cost-effective first repair to attempt.
- Have the engineer inspect the gas valve and verify correct gas pressure at the burner Gas Safe engineer
If the electrode and wiring are in good condition, the engineer should check that the gas valve is opening correctly and that gas pressure at the burner is within Protherm's specified range. An incorrectly functioning gas valve can produce a flame that is too weak or unstable for the ionisation circuit to read reliably. Gas valve work is legally required to be carried out by a Gas Safe registered engineer.
- Request a PCB diagnostic if other components test as serviceable Gas Safe engineer
If the gas supply, ionisation electrode, wiring, and gas valve have all been checked and found to be in order, the engineer should test the PCB's ability to process the flame signal. PCB replacement is a higher-cost repair and should only be recommended once other causes have been confidently ruled out. An experienced engineer may test the PCB's signal outputs before committing to replacement.
- Call a Gas Safe registered engineer if the fault persists after your initial checks Gas Safe engineer
If a reset and gas supply check have not resolved F.07, this fault requires professional diagnosis. Do not continue resetting the boiler repeatedly. Contact a Gas Safe registered engineer — you can verify an engineer's registration at gassaferegister.co.uk — and have your boiler model and the fault code ready when you call.
Parts you may need
- Ionisation electrode (flame-sensing electrode) · from £25
- Ignition electrode lead / HT lead · from £20
- Gas valve · from £130
- PCB (main control board) · from £280
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
Is the Protherm F.07 fault dangerous?
F.07 is a safety lockout, which means the boiler has shut itself down rather than continuing to operate without confirmed flame detection. This is the correct and safe response — unburnt gas is not being allowed to accumulate. The boiler is not actively dangerous in its locked-out state, but you should not attempt to repeatedly force-reset it or bypass any safety controls. Leave investigation to a Gas Safe registered engineer.
Can I fix F.07 myself?
There is very little a homeowner can safely do beyond confirming the gas supply is on and attempting one or two resets. Accessing the combustion chamber, inspecting or cleaning the ionisation electrode, testing the gas valve, or working on the PCB all require either Gas Safe registration (for anything involving gas) or specialised electrical knowledge. Attempting these repairs yourself is both unsafe and, in the case of gas components, illegal in the UK.
How much does it cost to fix a Protherm F.07 fault?
The most common repair — cleaning or replacing the ionisation electrode and its lead — typically comes to between £120 and £200 all-in including the engineer's call-out. A gas valve replacement tends to fall in the £200–£350 range. If the PCB turns out to be the cause, replacement costs can rise to £500–£700 or more for parts and labour, which on an older boiler may prompt a conversation about whether full boiler replacement represents better value.
Why does my Protherm boiler keep showing F.07 after I reset it?
If F.07 returns shortly after every reset, the underlying fault has not been resolved — you are simply clearing the lockout temporarily. The most likely explanations are a degraded ionisation electrode that can no longer produce a reliable signal even when the flame lights, an intermittent wiring fault in the electrode lead, or a gas supply issue that comes and goes. Repeated resets without a proper fix can occasionally stress the ignition components further. Arrange for a Gas Safe engineer to diagnose the root cause rather than continuing to reset.