No Hot Water
Gas Safe Reg. 980201• Same-day across Bradford, Leeds & Yorkshire
On a combi boiler, no hot water (but heating still works) almost always points to the diverter valve, the flow sensor or the plate heat exchanger. On a system or regular boiler with a cylinder, it's usually the immersion, motorised valve or thermostat. Either way — same-day fix in most cases.
Most likely causes
- 1Diverter valve stuck on heating side (most common combi fault)
- 2Flow sensor or turbine fault — boiler not detecting tap demand
- 3Scaled or blocked plate heat exchanger (hard-water areas)
- 4Faulty motorised 3-port valve (system / regular boilers)
- 5Cylinder thermostat or immersion failure (regular boilers with a tank)
- 6Low pressure causing combi to lock out hot-water demand
What you can safely check first
Sometimes one tap's cartridge has failed. If hot water flows from the kitchen sink but not the bathroom — it's a tap issue, not the boiler.
If the boiler pressure has dropped below 0.5 bar, the boiler may refuse to heat water. Top up to 1.0–1.5 bar.
Run a hot tap for 30 seconds — does the boiler fire up? If yes but water is cold, it's a heat-exchanger or flow issue. If no fire-up, it's electronic.
- Vulnerable person without hot water for bathing or formula
- Boiler showing fault code or repeated lockouts
- Water coming out scalding then freezing — diverter risk
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