No heating because boiler pressure is too low
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Most likely cause & what to check
Check the pressure gauge on the front of the boiler — it should read between 1 and 1.5 bar when cold. Below 1 bar and many boilers will lock out and stop heating.
Locate the filling loop — this is usually a small braided hose or rigid bar with two valves, located under the boiler. Sometimes hidden behind a panel.
Open both valves slowly (turn them so the slot runs in line with the pipe). You will hear water entering the system.
Watch the pressure gauge — when it reaches 1.2–1.5 bar, close both valves firmly.
Press the reset button on the boiler and wait for it to fire up. Heating should resume within a few minutes.
Check the area around the filling loop and under the boiler for any drips — if the pressure drops again within a few days, there is a leak or fault that needs investigating.
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Frequently asked questions
How do I know which boiler has a filling loop?
Sealed system boilers and combi boilers have filling loops. Open-vented systems with a cold water tank in the loft do not — they are refilled automatically from the tank.
What happens if I overpressurise the boiler?
Above 3 bar the pressure relief valve will open and release water outside. If this happens, let the system cool, then bleed a radiator to reduce the pressure to 1.2–1.5 bar.