One zone not heating — upstairs or downstairs cold
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →If one floor of your house has gone cold whilst the other is toasty warm, a zone valve fault is almost certainly to blame. Zone-based heating systems are brilliant for comfort and efficiency — they let you heat upstairs and downstairs on separate schedules — but when a motorised zone valve fails, that whole zone drops off the heating circuit. This problem is incredibly common in homes with two-zone systems, especially after 10–15 years of use. The good news is that the fault is usually straightforward to diagnose and repair without major disruption. This guide walks you through checking the zone valve, testing it safely, and understanding what a replacement involves. If you're not confident working around your boiler or handling valves, it's worth calling a Gas Safe registered engineer — they'll have the part fitted within an hour.
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Most likely cause & what to check
Zone-based heating systems use motorised zone valves (typically two-port valves, 22mm or 28mm) to direct hot water to upstairs and downstairs independently. A failed zone valve is the most common cause of one zone not heating.
Go to the boiler cupboard and listen when the affected zone calls for heat — you should hear a click from the zone valve as it opens. No click suggests the valve motor has failed.
Check the thermostat for the affected zone — confirm it is set above the current temperature.
On some zone valves there is a manual lever on the side. Pushing this open bypasses the motor and allows you to confirm if the valve mechanics are working. Do this as a temporary test only.
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Frequently asked questions
How do I know if it's actually a zone valve and not something else?
Zone valves sit on the pipework near your boiler and look like motorised ball valves with a small electric motor head bolted on top. If you have a heating system that lets you control upstairs and downstairs separately via two different thermostats, you definitely have zone valves. If only one floor is cold and the boiler is firing up normally, a failed zone valve is the prime suspect.
Can I fix a zone valve myself, or do I need an engineer?
You can safely diagnose the problem yourself — listening for the click and checking the manual lever are low-risk tests. However, actually replacing the motorised head is best left to a plumber or heating engineer because it involves draining part of the system and ensuring the valve is correctly reassembled. This typically takes under an hour and costs £25–£60 for the part.
What's that clicking sound I hear near the boiler, and does it mean the valve is working?
That click is the zone valve motor opening or closing the valve as the thermostat calls for heat. If you hear it when the cold zone calls for warmth, the motor is likely working fine — the problem may be elsewhere. If there's no click at all, the motor has almost certainly failed and needs replacing.
Is it safe to push the manual lever on the zone valve?
Yes, pushing the manual lever is safe and is a recognised diagnostic test. It bypasses the motor and allows water to flow through the valve, which confirms whether the valve mechanics themselves are sound. However, treat it as a temporary test only — you should switch the manual lever back and get the motor replaced rather than relying on it long-term.