No Hot Water: Common Causes and What to Check

What to check first

No Hot Water: What to Check First

Look at the boiler display or indicator lights first. Most modern boilers show a fault code when there is a problem, so note the code and look it up in your boiler manual or against your boiler brand name. Common codes relate to low pressure, ignition failure, or a sensor fault. A reset (usually a button on the front panel) sometimes clears a temporary fault, but if the same code returns within an hour there is an underlying issue for a plumber or gas engineer.

Then check the boiler pressure. Most combi and system boilers need 1 to 1.5 bar to fire, and if the gauge sits in the red zone the boiler locks out. To repressurise, open both valves on the filling loop slowly until the gauge reads 1 to 1.5 bar, then close them firmly. Finally, check the programmer or timer, as a power cut or a knocked schedule can leave hot water switched off for the current time period.

• Check the boiler display for a fault code
• Check boiler pressure and aim for 1 to 1.5 bar
• Check the programmer and timer settings
• Try a boiler reset once
• Switch on the immersion as a backup

Cylinder or combi

Cylinder, Immersion or Combi

Homes with a system boiler or back boiler store hot water in a cylinder, usually in the hot press. If the boiler is running but the water stays cold, the cylinder thermostat may have failed, or the motorised valve that sends hot water to the cylinder may be stuck. You can switch the immersion heater on for about 45 minutes as a temporary backup: if hot water returns, the fault is with the boiler or its controls, not the cylinder itself.

A combi boiler heats water on demand and has no cylinder, so there is nothing stored to reheat. With a combi, no hot water usually points back to the boiler, its pressure, or the programmer rather than a separate hot water circuit. Knowing which type you have narrows down where the fault is likely to be before a plumber calls out.