No Hot Water from Boiler: Causes & Fixes

Your heating works but you have no hot water? Or neither is working? Here are the most common causes and what you can do.

If your heating works but you have no hot water

This is the most common scenario, and on a combi boiler it usually points to one of these:

1. Faulty diverter valve

The diverter valve switches the boiler between heating and hot water. If it's stuck in the heating position, you'll have heating but no hot water. This is the most common cause.

Fix: The diverter valve needs replacing — call a Gas Safe engineer.

2. Blocked plate heat exchanger

The plate heat exchanger heats the domestic hot water. If it's blocked with sludge or scale, hot water won't flow through it properly.

Fix: The plate heat exchanger needs cleaning or replacing — call a Gas Safe engineer.

3. Faulty hot water sensor

If the hot water temperature sensor (NTC) is faulty, the boiler may not know when to fire for hot water.

Fix: The sensor needs replacing — call a Gas Safe engineer.

4. Crossed pipework

If the hot and cold pipes were crossed during installation, the boiler won't get the correct flow signal.

Fix: The pipework needs correcting — call a Gas Safe engineer or your installer.

If you have no heating AND no hot water

1. Boiler not firing at all

Check:

• Is the boiler switched on at the spur?
• Is the boiler displaying a fault code? (Check our fault code guides for Vaillant, Worcester Bosch, Ideal, Baxi, Glow-worm)
• Is the gas supply on?
• Is the boiler pressure between 1.0 and 1.5 bar?

2. Frozen condensate pipe

In freezing weather, the condensate pipe outside can freeze and block, causing the boiler to lock out. Pour warm (not boiling) water over the pipe to thaw it.

3. Gas supply issue

Check that other gas appliances are working. If they aren't, the issue is with your gas supply — contact your gas supplier.

4. Power cut or tripped switch

Check that the boiler has power — check the fused spur switch and your consumer unit for tripped switches.

Quick checks you can do yourself

1. Check the boiler pressure — Should be 1.0–1.5 bar.
2. Check for a fault code — Look up the code in our fault code guides.
3. Reset the boiler — Try resetting after checking pressure and gas supply.
4. Check the condensate pipe — In cold weather, check for a frozen pipe.
5. Check the thermostat and programmer — Make sure they're calling for heat/hot water.

Need help with no hot water?

Sanju's Heating covers Newbury, Basingstoke and Reading. Call us on 01635 74 50 40 or book online at sanjusheating.co.uk/book