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BoilerCodes

No heating? Work through these checks

When the radiators stay cold, the cause is often a setting rather than a broken boiler. These are the checks the manufacturers suggest, in a sensible order.

Checks to do first

  1. Look at the display. If there's a fault code, look it up here. Vaillant, Viessmann, Glow-worm
  2. Check the heating is switched on at the boiler and controls, and not set to hot water only. Glow-worm, Vaillant, Viessmann, Vokera
  3. Check the timer or programmer is in an on period. A power cut or the clocks changing can reset it. Vaillant, Ideal, Viessmann, Worcester Bosch, Vokera
  4. Turn the room thermostat up above the current room temperature. If it's set lower than the room, the heating won't come on. Ideal, Viessmann, Worcester Bosch, Vokera
  5. If your thermostat runs on batteries or talks to a receiver by the boiler, change the batteries and check the receiver is working. Vaillant, Glow-worm, Viessmann, Ideal
  6. Check the boiler has power and the gas is on (try the hob, and check a prepayment meter has credit). See boiler display blank. Vaillant, Viessmann, Ideal, Worcester Bosch
  7. Check the pressure gauge with the heating cold and top up if it's low. our pressure guide gives your brand's figure. Vaillant, Ideal, Viessmann, Worcester Bosch
  8. Make sure the radiators themselves are turned on, including any thermostatic valves on them. Ideal, Glow-worm
  9. In freezing weather, check the condensate pipe outside and thaw it safely if it's frozen. Vaillant, Worcester Bosch, Baxi, Ideal
  10. Once you've fixed the cause, reset the boiler as your manual describes. Vaillant, Baxi, Viessmann

Hot water works but the heating doesn't

Some radiators warm, some cold?

That's usually air or sludge rather than the boiler. See radiators cold in places.

Call a Gas Safe engineer if

Find a Gas Safe engineer near youOpens the official Gas Safe Register search.

The names after each step are the manufacturers whose own guidance backs it. Every boiler is different, so check your manual too.

Common questions

Why is my boiler on but the radiators are cold?

Manufacturers say the most common reasons are settings: the heating set to hot water only, the timer in an off period, or the thermostat set below the room temperature. Check those before assuming a fault.

Can a power cut stop my heating?

Yes. Vaillant, Ideal and Viessmann all say a power cut or clock change can reset the boiler's timer, so check the time and programme after the power comes back.

Sources