Stuck Diverter Valve
Hot water that is lukewarm, briefly hot then cold, or only works when the heating is off..
Hot water that is lukewarm, briefly hot then cold, or only works when the heating is off.
What is actually going on
Hot water that is lukewarm, briefly hot then cold, or only works when the heating is off.
The realistic causes, in order
A seized valve cartridge or ball, usually from scale or sludge deposits around the seat A failed motor or micro-switch on the valve head, so the boiler never learns the valve has moved A worn valve seal allowing heated water to bypass towards the heating circuit
What we test on site
Valve movement observed directly while switching between heating and hot water demand Micro-switch continuity and the signal the PCB actually receives Whether radiators warm up while a hot tap is running, which proves the bypass
Questions we get asked
What causes a stuck diverter valve on a gas boiler?
A seized valve cartridge or ball, usually from scale or sludge deposits around the seat
What normally puts a stuck diverter valve right?
A head or cartridge replacement resolves this on most makes without disturbing the rest of the system.
Is it safe to keep using the system with a stuck diverter valve?
Working on the water side of a boiler means draining and refilling correctly, then re-pressurising and re-commissioning — not a job to attempt with the case off.