Hot Water
No Hot Water? Causes and How To Fix It
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
No hot water from the taps has a handful of usual causes — a stuck diverter valve, a thermostat or timer setting, low pressure, or (on stored systems) the immersion. Here’s how to work through them safely.
Quick answer: If you have heating but no hot water, the diverter valve is the usual culprit. No hot water at all can be low pressure, a thermostat or timer setting, or — on stored-cylinder systems — the immersion or programmer. Check pressure and the timer first; a stuck diverter needs an engineer.
Common Causes
Why there’s no hot water
These are the usual causes, roughly in order. The colour on the left shows whether it’s a safe homeowner check or a job for an engineer.
| What you see | Likely cause | What to do |
|---|---|---|
| Heating works, no hot water | Diverter valve stuck | Needs an engineer to free or replace it |
| No hot water at all | Low pressure or lockout | Check the gauge; repressurise to ~1.3 bar |
| Hot water only lukewarm | Diverter partly stuck or scale | Book an engineer to check the diverter |
| No hot water, stored cylinder | Immersion or timer fault | Check the timer and thermostat; test the immersion |
| Hot then quickly goes cold | Flow rate or diverter fault | An engineer can diagnose it |
| No hot water in cold weather | Frozen condensate lockout | Thaw the external pipe, then reset |
Safe Checks
What you can safely check
Safe to check
- The pressure gauge reads ~1.3 bar (top up if low)
- The hot-water timer/programmer is set to come on
- The cylinder thermostat (if you have one) is set to about 60°C
- In winter, the external condensate pipe hasn’t frozen
Book an engineer if…
- You have heating but no hot water (classic diverter fault)
- Water is only ever lukewarm however long you run it
- You can smell gas — leave and call 0800 111 999
Engineer Insight
What we usually find
On combi boilers, ‘heating fine but no hot water’ is nearly always the diverter valve — it sticks on the heating position and won’t switch to hot water. It’s a common, fixable part. On stored-cylinder systems it’s more often the immersion, the cylinder thermostat, or the programmer. We confirm which before quoting.
Costs
What repairs typically cost
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
No hot water — your questions answered
Why do I have heating but no hot water?
On a combi boiler this is almost always the diverter valve — it’s stuck in the heating position and won’t divert to hot water. It’s a common, fixable part an engineer can replace.
Can low pressure cause no hot water?
Yes. If pressure drops too low the boiler locks out and won’t heat water or radiators. Top up to about 1.3 bar with the filling loop and see if it restarts.
My cylinder system has no hot water — what now?
Check the programmer is set to heat water and the cylinder thermostat is at about 60°C. If the boiler is fine, test the immersion heater as a backup. If unsure, we can diagnose it.
Why is my hot water only lukewarm?
Usually a partly-stuck diverter or scale in the heat exchanger. Both reduce how hot the water gets. An engineer can free the diverter or descale the exchanger.
How much does it cost to fix no hot water?
A diagnostic visit is typically £80–£120 in North London. A diverter valve replacement runs about £150–£320. You’ll always get an upfront quote first.
Related
Keep troubleshooting
The reverse problem — usually the diverter or thermostat.
Read guideHot WaterHot Water Slow to Heat UpDistance, scale and diverter causes of a slow supply.
Read guideHot WaterLow Hot Water PressureWeak flow at the hot taps — scale and mains causes.
Read guidePressureLow Boiler PressureA common reason the boiler won’t heat water at all.
Read guideHeatingHeating Not WorkingIf heating’s affected too, start with the full guide.
Read guideFault CodesBoiler Fault Code LibraryLook up a hot-water fault code by brand.
Browse codesHead back to the Help & Advice Centre for more boiler and heating guides.
No hot water? We’ll get it back.
Book a Gas Safe engineer to check the diverter, immersion or pressure, or call and tell us what’s working and what isn’t — we’ll give you an honest steer first.
Gas Safe Registered 918817 | North London specialists | Upfront pricing