Your boiler keeps turning on and off and you need it to stop now, not after guesswork.
Boiler fires for 10–60 seconds, shuts off, then restarts again and again.
Is this your problem?
What to do
- Check boiler pressure first.
Look at the gauge. It should sit around 1.0–1.5 bar when cold.
If it’s below 1 bar, top it up using the filling loop, slowly.
Stop at 1.3 bar. Close valves fully. - Bleed one radiator only (nearest to boiler).
Air in the system causes rapid cycling.
Bleed briefly, then re-check pressure and top up again if needed. - Reset the boiler once.
One reset only. Repeated resets hide the real fault.
Safe DIY. Stop if pressure won’t hold. Call an engineer.
Radiators warm at the bottom but cold at the top, boiler keeps cutting out.
Is this your problem?
What to do
- Bleed all radiators properly.
Start downstairs, work up.
Towel + bleed key. Short hiss only. - Refill system pressure after bleeding.
Again, aim for 1.2–1.5 bar cold. - Run heating for 10 minutes and listen.
Cycling often stops once air is removed.
Safe DIY. If one radiator keeps filling with air, stop and call a pro.
Boiler cycles more when hot water is on.
Is this your problem?
What to do
- Check tap flow.
Turn hot tap halfway, not full blast.
If cycling reduces, flow sensor or plate heat exchanger may be blocked. - Try another hot tap.
Same issue = internal blockage likely. - This often happens when boiler pressure drops overnight
Not DIY beyond this. Engineer needed for internal parts.
Boiler cycles only when heating is on, hot water is fine.
Is this your problem?
What to do
- Check thermostat location.
If near a radiator or draught, it shuts boiler off too early.
Temporarily turn stat up by 2–3°C and test. - Check radiator valves.
Make sure at least one radiator has no TRV (usually hallway).
This prevents rapid temperature spikes.
Safe DIY. Permanent stat relocation needs an engineer.
Boiler pressure rises when heating is on, then drops after cooling.
Is this your problem?
What to do
- Watch pressure while heating runs.
If it climbs above 2.5–3 bar, expansion vessel is failing. - Look for water from the external copper pipe.
Dripping = pressure relief valve activating.
Stop here. This is not DIY. Call a Gas Safe engineer.
Boiler cycles constantly in cold weather only.
Is this your problem?
What to do
- Check condensate pipe outside.
If frozen, pour warm (not boiling) water over it. - Reset once after thawing.
Safe DIY. If it refreezes repeatedly, pipe needs insulating or rerouting.
When to stop and call a professional immediately
- Pressure won’t stay stable
- Boiler locks out repeatedly
- Loud banging or kettling noises
- Water leaking under the boiler
- Any gas smell (turn off and ventilate)