Your boiler is making hot water, but the radiators stay cold, that’s a very common and very fixable UK heating problem.
Is this your problem?
Hot taps work fine, but none of the radiators heat up.
What to do
• Check the boiler display and make sure heating is switched on, not hot-water-only.
• Turn the room thermostat above 20°C and wait a few minutes.
• If the boiler fires, it was a settings issue.
Safe DIY.
Is this your problem?
Some radiators heat up, others stay cold.
What to do
• Bleed the cold radiators using a radiator key.
• Let air out until water runs steadily, then close the valve.
• Check boiler pressure and top up to around 1.0–1.5 bar.
Safe DIY. Stop if pressure won’t hold.
Is this your problem?
One radiator stays cold while all others are hot.
What to do
• Make sure both radiator valves are fully open.
• Bleed the radiator, even if it doesn’t sound full of air.
• Gently open the lockshield valve if it’s been closed.
Safe DIY.
Is this your problem?
Radiators are warm at the top but cold at the bottom.
What to do
• This usually means sludge inside the system.
• Bleeding will not fix this.
• The system needs a power flush.
Not DIY. Call a heating engineer.
Is this your problem?
Radiators were working before, now none heat up after summer.
What to do
• Check the boiler pressure gauge. Below 1 bar will stop heating.
• Use the filling loop to raise pressure to about 1.2 bar.
• Restart the boiler once.
Safe DIY if you know where the filling loop is.
Is this your problem?
Radiators only heat when hot water is turned off.
What to do
• This points to a faulty diverter valve in a combi boiler.
• The boiler can’t send heat to radiators properly.
Not DIY. Book a Gas Safe engineer.
Is this your problem?
Upstairs radiators heat, downstairs stay cold.
What to do
• This is usually a balancing issue.
• Slightly close the lockshield valves on hot radiators.
• Leave cooler radiators more open.
DIY if confident. Stop if unsure.
Is this your problem?
Hot water works, radiators don’t, and you’re worried it’s dangerous.
What to do
• In most UK homes, this is not dangerous on its own.
• Boiler safety systems still control gas and temperature.
• Causes are usually air, pressure, valves, or controls.
When to stop and call a professional
• Boiler keeps locking out or showing fault codes.
• Loud banging, kettling, or burning smells.
• Pressure rises above 2.5–3 bar repeatedly.
• Any gas smell — turn the boiler off and call a Gas Safe engineer.
If none of these apply, it’s a heating fault, not an emergency.
How much does it cost to fix this problem in the UK?
If your boiler heats water but not radiators, UK repair costs usually fall between:
£60 – £250 (most common fixes)
Typical Costs:
- Bleeding radiators / low pressure: £0–£60
- Thermostat or valve issue: £80–£200
- Pump or diverter valve fault: £180–£350
- Powerflush (sludge blockage): £300–£600
Quick Tip:
Check boiler pressure (1–1.5 bar) and bleed radiators first — this fixes many cases for free.