divertor-valveCould your boiler’s diverter valve be faulty?

In this article, we’re going to explain what a diverter valve is, how it works, and what the signs are when it is not working correctly, along with possible solutions.

What is a diverter valve?

Your combi boiler diverter valve is a valve that opens and closes to provide heat to the radiators or to heat your water.

The diverter valve will always give priority to your hot water, so if you turn your heating on, and then a hot tap, it will heat the water to the tap first.

How to diagnose a faulty diverter valve

If when you turn on your tap and find you are not getting hot water, it may be because the valve is jammed and not working properly.

Another sure-fire sign is having to turn on the heating in order to get hot water to come through the tap. This means the valve is jammed open in the heating mode.

If you are getting all the hot water you need, but no heating, first check all your time clocks and controls are working. If everything else is fine, it’s almost definitely the case that the valve is not opening for the heating.

What should I do now?

Now that you’ve diagnosed the problem, you should call out a gas safe registered engineer to come and replace the diverter valve or service the working parts of the valve.

On a boiler under eight years old, this should be a routine fix and should not take any longer than an hour, as parts should be readily available.

However, a combi boiler over eight years old may be harder to source parts for and this is also a sign that other parts of your boiler could be wearing out.

How much will it cost?

A combi boiler diverter valve should cost between £100 – £150, plus the cost for labour and time. Taking that into account, it should cost you around £250 to get your faulty diverter repaired. It should also come with a parts and labour guarantee for between 3 – 12 months, although this could depend on the age of your boiler, as some parts may be close to breaking down.

If you are on a service plan this would cover the cost, however if your boiler is old and you need replacement parts quite often, it may be wise to consider replacing it.

A replacement boiler would be more cost effective over time, and because warranties last up to eight years, you may not even need a service plan. You’d also notice the difference on your monthly heating bills.


If you aren’t sure whether your diverter valve is working properly, it’s fairly easily to diagnose the problem. Tell-tale signs include having to turn on the heating to get hot water, or having plenty of hot water but no heating.

Your diverter valve should cost around £250 to repair with a gas safe registered engineer.

However, if your boiler is old and frequently experiencing problems, you may want to consider a replacement which could save you money in the long run.

Are you having problems with your old combi boiler and thinking of investing in a new one?