Fault guide
Combi boiler: no hot water, or hot water that goes hot and cold
If your heating works but the taps run cold, or the hot water keeps going hot and cold, the fault is usually in the part of the combi that heats water on demand.
Phones answered 7am–8pm, 7 days a week. Gas Safe registered 943380.
Further work and parts are always priced and agreed before we carry on.
What it means
A combi boiler sends heat either to the radiators or to a plate heat exchanger for your hot water. When the hot water side fails, the heating can carry on working normally.
Common causes
- Diverter valve sticking or worn
- Limescale in the plate heat exchanger. Portsmouth, Southampton and Surrey all have hard water.
- Flow sensor or hot water sensor fault
- Low pressure or a lockout code
- Hot water temperature set too low
Safe checks you can do
- Check the hot water temperature setting on the boiler.
- Check the pressure gauge on the front of the boiler. With the heating cold, it should usually read between 1 and 1.5 bar.
- Try a different tap at full flow. Some combis won’t fire on a very low flow rate.
- Note any fault code on the display before you call us. It speeds up the diagnosis.
When to call an engineer
If the checks above don’t clear it, or the fault keeps coming back, the boiler needs a Gas Safe engineer to diagnose it. Our diagnostic visit is £144 including VAT, covering attendance and up to the first hour. We tell you the repair price before doing any further work.
When you call, tell us the boiler make and model, the exact code on the display and what you have already tried.
Other guides
- Worcester Bosch EA 227
- Ideal boiler F2 and L2
- Vaillant F28 and F29
- Baxi E133 and E119
- Boiler losing pressure
Need a repair? Boiler repair in Portsmouth · Southampton · Guildford