Why Is My Hot Water Not Working but the Heating Is?
If your radiators heat up fine but you have no hot water, the problem is usually a diverter valve, a thermostat, or a hot water cylinder issue - not the boiler itself.
Combi boiler: check the diverter valve
On a combi boiler, a diverter valve switches between heating mode and hot water mode. If the valve gets stuck in the heating position, the radiators work but the hot water does not. This is one of the most common combi boiler faults. Signs include: hot water that works intermittently, hot water that only works when the heating is on, or radiators that get hot when you turn on a hot tap.
A stuck diverter valve is a straightforward repair for an engineer. The valve or its motor can usually be replaced without changing the whole boiler.
System boiler: check the cylinder thermostat
On a system boiler with a hot water cylinder, the cylinder has its own thermostat. If the thermostat fails or is set too low, the boiler will not fire to heat the cylinder even though it fires for the radiators. Check the cylinder thermostat is set to about 60°C. If it is set correctly but the water is still cold, the thermostat likely needs replacing.
Check the programmer
Some programmers have separate controls for heating and hot water. Check that hot water is set to ‘on’ or ‘auto’ and not accidentally switched off. After a power cut, the settings may have reset.
Motorised valve problems
If your system uses motorised zone valves (common in older systems with separate heating and hot water zones), the hot water valve may have failed. You can sometimes hear a motorised valve clicking or humming when it is trying to open. If it is stuck, the hot water circuit stays closed.
When to call us
If the quick checks above do not resolve it, the issue is almost certainly a faulty component - a diverter valve, cylinder thermostat, motorised valve, or the boiler’s PCB. These are not DIY jobs. Call us on 01932 943 009 and we will diagnose and fix it. Most hot water faults can be repaired in a single visit.
Need help with this?
Call us on 01932 943 009 or email info@hphsolutions.co.uk. We cover Surrey, Hampshire, Berkshire and London. Free quotes, no obligation.
