No hot water but heating works? Causes and what to do
If you have heating but no hot water, the cause is often a diverter valve, immersion or setting. Here is what to check and when to call an engineer.
Losing hot water is frustrating, especially if the heating is still working fine. The good news is that when radiators heat up but the taps run cold, the boiler itself is usually fine — the issue is typically a component that directs the hot water or a setting on the system.
Here is how to check the likely causes and when to call a Gas Safe engineer.
Check the easy things first
Before anything else, rule out the simple causes:
- The boiler controls — make sure hot water is scheduled and set to on, not just heating.
- The thermostat — check it is set high enough to heat the water.
- The immersion heater — on systems with a hot water cylinder, it may need to be switched on or may have tripped.
- A recent power cut — the timer or programmer may need resetting.
A surprising number of “no hot water” problems are just a setting that has been changed.
Common causes when heating works but hot water does not
If the settings are correct, the likely causes include:
- A faulty diverter valve, which directs water to the taps instead of the radiators.
- A faulty motorised valve on systems with a hot water cylinder.
- A failed immersion heater element or thermostat.
- A problem with the boiler’s hot water circuit or a blocked heat exchanger.
These are components that a qualified engineer should inspect rather than attempt as a DIY job.
When to call an engineer
Call a Gas Safe engineer if:
- The settings are correct but there is still no hot water.
- You hear unusual noises or the boiler keeps resetting.
- You suspect a gas or boiler fault.
- You smell gas — turn off the gas and call a professional immediately.
A quick, well-triaged response matters when hot water is off. Our guide to a good 24/7 call-out process explains what to expect when you book an urgent visit.
Getting it fixed
If your boiler is not producing hot water, our heating service covers repairs, servicing and installations for homes, landlords and businesses across London. Get in touch via our contact page and we will get the hot water flowing again.
All gas work should be carried out by a registered engineer — you can check anyone on the Gas Safe Register.
