Look up what your boiler or radiators are doing
A UK reference to boilers and central heating, built from makers' user manuals and official sources. Start with what you can see.
- A code is on the displayFind your maker's list
- Pressure gauge is lowWhat it should read
- Radiator cold at the topTrapped air
- Radiator cold at the bottomSludge
- It stopped in a freezeFrozen condensate pipe
- You can smell gasWhat to do, first
- A CO alarm is soundingWhat to do, first
- Something elseThe full look-up, by what you can see
Featured entry: Boiler pressure
Boiler pressure is the water pressure in a sealed heating circuit, and the right reading depends on the model, because manuals differ on when to top up and what to fill to. Read the entry
Worth knowing
- Worcester's Greenstar 24/28 manual says the pump runs when the boiler falls below 8°C and it fires below 5°C, as long as it has power. See the entry
- HSE puts deaths from carbon monoxide from gas appliances and flues at around 7 people a year. See the entry
- The Boiler Upgrade Scheme covers England and Wales only, at £7,500 for an air source heat pump as read on 3 November 2026. See the entry
- Reset methods vary even inside one maker's range, from a quick press to several seconds on two keys. See the entry
Read the display
F.22VaillantEAWorcester BoschE133BaxiL2IdealF.28Glow-wormCLViessmannSubjects
Boiler types
What sort of boiler and hot water set-up a house has.
Pressure and water
The gauge, the filling loop and where the water goes.
Fault codes by maker
What each maker's own user manual says a display means.
Radiators
Bleeding, balancing, cold patches, sludge and noise.
Controls
Valves, thermostats, timers and flow temperature.
Cold weather and hard water
Frozen condensate, frost, limescale and sea air.
Safety and the law
Gas smells, carbon monoxide, registered engineers, landlords.
Replacing and paying
Quotes, building rules, grants, heat pumps and running costs.