No heat or hot water? How to diagnose boiler problems

Read on to discover how to diagnose the most common boiler problems and how to fix them.


How to diagnose boiler problems: white boiler on a blue wall

Key steps

  • Got hot water but no heating? Try bleeding or cleaning your radiators.
  • Think your boiler is working, but no water is coming out? Check for error codes, and double check the timer.
  • Check the central heating or hot water isn't accidentally switched off.
  • If other methods don’t work call a gas safety registered engineer.

The first sign that you’re having boiler problems is usually that the central heating, hot water, or both, stop working. Sometimes these issues are easy to fix yourself, and sometimes you'll need to call in a professional. Here we’ll go through a step-by-step process for working out what’s wrong when your boiler is not heating water or the central heating is playing up.

While these boiler problems are easy to diagnose and fix, there are other things that could go wrong. Read our advice on how to avoid a meltdown during boiler problems.

Diagnosing boiler problems: 2 common faults when you find your boiler’s not working

There are two very common boiler problems, both of which can actually be fixed easier than you may realise. Here are our top tips to diagnosing the issue when you discover your boiler not working properly.

1. You’ve got hot water but no heating

If your boiler is providing you with hot water but not central heating, there are a couple of things you should check before calling out an engineer.

  • Your radiators need bleeding. We have a guide to do this yourself here.
  • Your radiators need cleaning. Read how to do this here.
  • Your central heating needs turning on. If you’ve had a power cut it could lead to timers, thermostats and more being reset. Simply set them back up.
  • You have low water pressure. Try resetting your boiler.
  • Your boiler had broken diverter valves. If the above methods have not fixed your heating, it is likely to be a broken diverter valve. This should only be fixed by a gas safety registered engineer, so it’s time to call in a professional.

2. You’ve got no hot water from the boiler but the heating is working

If your hot water’s not working, you’ll be looking at some cold baths and showers! Here are a few things to try if your boiler is working but no hot water is coming out of your taps:

  • If your boiler is not heating water, first check for an error code, as some boilers may display these. If it does, it will be a lot easier to diagnose.
  • Check the timer. Most boilers have timers, and some have a separate heating timer for water. If this has been adjusted or reset, possibly due to a power cut, it may be a simple fix.
  • Check the water heater is on. If you’re getting no hot water from the boiler but the heating is working fine, first check if the hot water settings have been turned off by accident.
  • Again, it could be a diverter valve. Just like when you have hot water but no heating, if the hot water’s not working it could be thanks to a broken diverter valve. Call a gas safety registered engineer to get this fixed.

Should you replace the boiler?

While these two common faults can be easily fixed either by yourself or a gas safety registered engineer, you should consider whether your boiler actually needs replacing. Old boilers can lead to more issues than you want to be fixing, and also don’t run as efficiently. If your boiler is ten years old or more, consider getting it replaced.   So, if your boiler’s not working, now you can work out what’s wrong – and what to do about it – with our guide!

Originally published