The short answer
F2 on an Ideal Logic means the flame lit but then went out while the boiler was running. L2 is the other way round: the boiler could not light at all. The usual causes of F2 are a gas supply that dips under load, a blocked or damaged flue, a failing fan, a sticking gas valve or a worn flame-sensing electrode. Check your gas supply and condensate pipe, reset once, and call an engineer if it returns. Typical London repair: £90 to £400.
What the law requires
What does F2 mean on an Ideal boiler?
F2 is the flame loss code on Ideal Logic boilers. The burner ignited, the control board saw the flame, and then the flame disappeared or the board stopped being able to detect it. The boiler shuts the gas and locks out.
This is the part people mix up. On the Logic family, F2 means the boiler lit and then lost the flame, while L2 means it never lit. Ideal’s own fault page groups both under “flame loss or ignition lockout”, which blurs the difference, but the practical meaning matters for diagnosis. If your display says F2, you had heat for a while before it failed. If it says L2, nothing ever caught. Our Ideal L2 guide covers that one.
Because the flame was already established, F2 points at conditions that change during a burn: gas pressure under load, flue behaviour, fan speed and sensing.
Why does F2 happen?
This is safe to do yourself and needs no tools. The boiler case stays closed.
A gas supply that dips under load.
Prepayment meters running out of credit, a half-closed isolation valve, a failing meter regulator, or low inlet pressure on a shared supply when everyone fires their boiler at once. If the hob also burns weakly, the boiler is not the problem.
A blocked or damaged flue.
If the flue terminal is partly blocked, or the flue has separated at a joint, the burner is starved of air or products of combustion recirculate. F2 that only appears in windy weather is a flue issue until proven otherwise.
A faulty or misset fan.
The fan supplies combustion air. If it slows or surges, the flame lifts off the burner and goes out.
A sticking gas valve.
The valve may not open fully when demand rises, so the flame starves exactly when more gas is needed.
A worn flame-sensing electrode.
The flame is proven through a tiny current. As the tip erodes the signal weakens and the board decides the flame is gone. Common on Logics over six years old.
A frozen or blocked condensate pipe.
Backed-up condensate disturbs combustion. F2 on cold mornings that clears by lunchtime is the signature. Our frozen condensate guide covers the fix.
A poor earth connection.
Flame sensing needs a good earth. A corroded or loose earth bond causes false flame loss on an otherwise healthy boiler.
What you can safely do yourself
None of this involves opening the case.
- Check the gas. Light a hob ring. If it burns weakly or not at all, check your meter credit and the isolation valve by the meter, then call your gas supplier.
- Check the condensate pipe If it is frozen, pour warm (not boiling) water along it.
- Look at the flue terminal from the ground for debris, nests or anything stacked in front of it.
- Reset once. Press the reset button. If the boiler runs for twenty minutes without a fault, the cause was probably temporary.
- Stop there. If F2 returns within the hour or the next day, book a repair. Repeated resets against a real fault wear the electrode and gas valve.
Half the house cold? Describe which radiators and where they are cold, and we will usually name the fix on the phone.
What an engineer does on an F2 call
The engineer checks working gas pressure at the boiler with it running at full rate, inspects the flue end to end, runs a combustion analyser test, removes and inspects the electrode, and tests the earth. The fan and gas valve are checked only if everything else passes, with a fixed price given before any part is fitted.
How much does an Ideal F2 repair cost in London?
Fixed price quoted after diagnosis.
- Diagnosis and reset with a minor adjustment (earth, condensate clear): £90 to £140.
- Electrode replacement: £110 to £220 fitted.
- Flue clearance or repair: £120 to £400 depending on access.
- Fan replacement: £180 to £350 fitted.
- Gas valve replacement: £220 to £400 fitted.
- Condensate trap clean or reroute: £110 to £220.
The Logic is cheap to repair because parts are plentiful. On a boiler past twelve years old with a major fault, run the half-cost rule in our repair or replace guide.
Is F2 dangerous?
No. It is the safe state. The gas was shut off within a second of the flame being lost. The risk comes from the reaction: repeated blind resets, tampering with the flue, or opening the case. If you smell gas, leave the property and call the National Gas Emergency line on 0800 111 999.
Ideal F2, quick answers
What is the difference between F2 and L2?
F2: the flame lit then went out. L2: it never lit.
Why does F2 only happen on cold mornings?
Usually the condensate pipe.
Why does F2 only happen in the wind?
Usually the flue terminal.
How many resets are safe?
It will not fire while the fault is active. Top up and it runs.
Is my Logic worth repairing?
Almost always. Past twelve years with a major fault, run the half-cost rule.