Diverter valve fault — no hot water (combi boiler)
Check the steps below first — if you\'re not confident, get it fixed safely today.
Find a Gas Safe engineer near you →⚠️ Do not attempt to work on internal boiler components. All gas boiler repairs must be carried out by a Gas Safe registered engineer.
Not sure if this matches your problem?
Use our interactive tool — answer a few questions and get a personalised diagnosis.
Most likely cause & what to check
On a combi boiler, the diverter valve switches the heated water between the central heating circuit and the domestic hot water heat exchanger. When it fails, the symptoms are typically: no hot water despite heating working, or hot water that runs warm rather than hot.
A stuck-open diverter valve means heat goes to the radiators even when you only want hot water — and vice versa. You may notice radiators warming up when you run a tap.
This is an internal boiler component repair — only a Gas Safe registered engineer should open the boiler casing and replace parts.
Call a Gas Safe engineer and describe: "My combi boiler is heating the radiators fine but producing no hot water — I suspect the diverter valve." A new diverter valve typically costs £50–£150 for parts; labour brings the total to £150–£350.
While waiting for the engineer, you can temporarily use a portable electric heater or an electric shower if you have one fitted.
This job needs a qualified engineer — post it now
Post the job and we'll match you with vetted local engineers. Free, no obligation.
Find a Gas Safe registered engineer near you and get it fixed properly.
Was this guide helpful?