Vented system — boiler on but no hot water

🔒 Written by a Gas Safe registered engineer

May Need Pro💷 £0–£200⏱ 20 min–2 hrs

⚠️

This job may need a professional

Check the steps below first — if you\'re not confident, get it fixed safely today.

Safety First
⚠️ If you smell gas, do NOT attempt any fixes. Leave the property and call the National Gas Emergency Service: 0800 111 999.

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Most likely cause & what to check

Check the programmer or timer first — go to your programmer (usually on the wall near the boiler) and make sure hot water is scheduled to come on. It's very easy to accidentally switch it to heating-only.

Check the cylinder thermostat — this is the dial on the side of your hot water cylinder in the airing cupboard. It should be set to 60°C. If it's been turned down to a very low setting, the boiler won't fire for hot water.

Listen at the airing cupboard when hot water should be coming on — you should hear a motorised valve click and a faint whirring sound. If you hear the boiler fire but the water doesn't heat up, the motorised (zone) valve may be stuck in the closed position.

Try the immersion heater as a temporary backup — there should be a red-switched socket near the cylinder. Switch it on and leave for 45–60 minutes. If the water heats up, the problem is confirmed to be the boiler circuit rather than the cylinder itself.

Check the boiler display for any fault codes and look them up in our Boiler Fault Code tool.

Check the cold water storage tank in the loft is not empty — if it is, the cylinder won't refill and there will be no hot water. The ball valve in the tank may be stuck.

If the motorised valve is not clicking at all when hot water is called, it has likely failed and needs replacing — this is a job for a Gas Safe engineer.