Heating Not Coming On: Controls, Valves and Power
Heating that won't start while hot water works normally points away from the boiler and towards the controls and the heating circuit.
Heating that won't start while hot water works normally points away from the boiler and towards the controls and the heating circuit. A large share of these call-outs are resolved without any parts at all — flat thermostat batteries and programmers that reset after a power cut are genuinely common. The rest are usually a motorised valve or a pump.
Start with the controls
Wireless room thermostats run on batteries and lose their pairing when those batteries die. Programmers revert to default schedules after a power interruption. Smart controls can silently apply a holiday or geofence mode. Check the schedule, the set temperature, and whether the thermostat is calling for heat before assuming a mechanical fault.
Motorised zone valves
In systems with separate heating and hot water zones, a motorised valve directs flow. When the actuator fails or the valve body seizes, hot water continues to work and heating never gets flow. You can often hear a valve that is trying and failing to move. Many valves allow the head to be replaced without draining the system.
Pump and circulation
A pump that has seized after a summer of standing idle is a classic autumn fault. Sometimes it frees off, but a pump that has partially failed will circulate poorly and produce lukewarm radiators rather than none at all. We check pump speed setting as well as operation, because an incorrect setting causes both noise and poor performance.
Wiring centres and interlocks
Older systems have a wiring centre where thermostats, valves, pump and boiler meet. Loose terminals and corroded connections here cause intermittent faults that look like a failing boiler. Diagnosing at the wiring centre is often quicker and cheaper than replacing components one at a time.
Common questions
Why do I have hot water but no heating?
Most often a control fault or a motorised zone valve stuck in the hot water position. The boiler itself is usually fine, which is why diagnosis matters before anyone quotes for a replacement.
Could this be the thermostat?
Very often, yes — flat batteries, a lost wireless pairing, or a schedule reset. It's the first thing we check and the cheapest thing to rule out.
Should I upgrade to smart heating controls while you're here?
It can be worth it, particularly for zoned control in a larger house. We'll fit and configure them properly, including a correct interlock so the boiler isn't left short-cycling.
Do you work on systems you didn't install?
Yes. We service, repair and upgrade existing heating systems of all ages, not only our own installations.