No heating in one zone only — upstairs or downstairs
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Most likely cause & what to check
If your system has zone valves (motorised valves — usually 2-port or 3-port), each zone is controlled independently. A failing zone valve is the most likely cause of one zone not heating.
Listen near the boiler or airing cupboard when the affected zone calls for heat — you should hear a quiet click or motor sound as the zone valve opens. Silence suggests the valve is not operating.
Locate the zone valve for the affected circuit (usually labelled or colour-coded). Many zone valves have a manual lever override — with the boiler off, push this lever to manually open the valve and check if the circuit heats when the boiler is on.
If the radiators heat up with the valve manually overridden, the valve motor has failed and needs replacing. Zone valve motors are replaceable independently of the valve body.
Check the zone thermostat or programmer for that zone separately — confirm it's calling for heat. A zone that's always "satisfied" won't open its valve.
Check the wiring connections at the zone valve and zone control panel. A loose wire is a common cause of intermittent zone failure, especially in older systems.
Zone valves are typically replaced by a heating engineer and cost £30–£80 for parts plus labour. If the valve body itself is corroded or leaking, the whole valve assembly needs replacing.
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