emergency
Boiler on but no heating — Same-Day Plumber Across the North West
If your boiler is on but the radiators stay cold, we’ll help you get to the cause quickly and safely.
In short
A boiler can appear to be running while the heating stays off because of low pressure, a thermostat or timer issue, trapped air, a faulty valve or a circulation problem. KJ Plumbers can arrange a vetted subcontractor engineer across the North West to diagnose the fault, explain what has failed and provide a written fixed-price quote before any repair work goes ahead.
Tell KJ what's wrong
Free and no obligation — we'll get a qualified local plumber on it.
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Hi, I'm KJ — honest UK plumbing advice, free, and a local plumber when you need one. Tell me what's happening — leak, blockage, boiler, emergency, anything — and I'll help you sort it.
You can send a photo, short video, voice note or share your location — whatever's easiest. Please avoid sending faces, documents, house numbers or payment cards in photos.
For genuine emergencies call 01706 318200, or the National Gas Emergency Service on 0800 111 999.
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Immediate steps to keep you safe
Check for warning lights or fault codes
Look at the boiler display and note any fault code, flashing light or pressure reading. Do not remove the boiler casing, as internal boiler checks must only be carried out by a qualified heating engineer.
Confirm the heating controls are calling for heat
Make sure the thermostat is set above the current room temperature, the timer is on, and the heating mode is selected. If you have smart controls, check the app, batteries and Wi-Fi connection as well.
Look at the boiler pressure
Most sealed heating systems should sit around 1 to 1.5 bar when cold, but always follow your boiler manual. If pressure has dropped very low or keeps dropping after topping up, stop and arrange a proper diagnosis.
Do not keep resetting the boiler
One reset may clear a temporary lockout, but repeated resets can mask a fault and may put extra strain on parts. If the boiler keeps failing to heat, leave it and book an engineer visit.
Act quickly if you smell gas or fumes
If you smell gas, turn off the gas at the meter if safe, open windows, avoid switches and flames, and call the National Gas Emergency Service on 0800 111 999. If you suspect fumes or carbon monoxide, leave the property and seek urgent help.
Common causes
What's usually behind boiler on but no heating
Thermostat, programmer or smart control fault
The boiler may be ready to work, but the controls are not sending a demand for heating. Flat thermostat batteries, incorrect schedules, receiver faults and smart control connection issues can all leave the radiators cold.
Low system pressure
If the pressure is too low, many boilers will protect themselves by not firing correctly for central heating. Pressure loss can be caused by a small leak, recent radiator bleeding, a faulty pressure relief valve or an expansion vessel issue.
Diverter valve stuck or failing
On combi boilers, the diverter valve directs heat between hot water and central heating. If it sticks, you may still get hot water at the taps but no heating to the radiators, or the heating may only work intermittently.
Circulation pump problem
The pump moves hot water around the radiators. If it is seized, weak, airlocked or not receiving power, the boiler may fire briefly but the heat will not circulate properly through the system.
Air, sludge or a blocked heating circuit
Trapped air, dirty system water or sludge build-up can stop radiators heating evenly. You might notice cold spots, noisy pipes, some radiators working while others stay cold, or the boiler cycling on and off.
Motorised valve or zone valve issue
In systems with a hot water cylinder or multiple heating zones, a motorised valve may fail to open. The boiler may be on, but heat is not being allowed through to the central heating circuit.
How KJ handles this
What happens when we're on-site
- 1
Confirm the symptom and system type
The engineer will ask what is and is not working, such as hot water, upstairs radiators, downstairs radiators or specific zones. They will identify whether you have a combi, system or regular boiler and how the controls are set up.
- 2
Check controls and demand for heat
They will test the thermostat, programmer, receiver, wiring centre where accessible and heating demand signal. This helps separate a control fault from a boiler or circulation fault.
- 3
Inspect pressure, visible pipework and radiator behaviour
The engineer will review system pressure, look for signs of leaks or discharge, and check whether radiators are cold throughout, partially warm or affected by air. These clues point towards pressure loss, airlocks, sludge or flow restrictions.
- 4
Test circulation and key heating components
Depending on the system, checks may include the pump, diverter valve, zone valves and temperature rise across the heating flow and return. The aim is to find whether heat is being produced but not moved around the system.
- 5
Assess boiler fault codes and safe operation
Any displayed fault codes will be checked alongside safe operating checks. The engineer will not rely on guesswork; they will use the boiler’s behaviour and measurements to identify the likely failed part or system issue.
- 6
Provide a written fixed-price repair quote
After the diagnostic visit, the engineer will explain the findings and provide a written fixed-price quote for any repair. You can then decide whether you want the work to proceed.
Where we cover
North West England — same-day where possible
FAQ
Frequent questions
Why is my boiler on but there is no heating?
Common reasons include the thermostat not calling for heat, low boiler pressure, a stuck diverter valve, a faulty pump, trapped air, sludge or a motorised valve problem. The exact cause depends on whether you still have hot water and whether all radiators or only some are affected.
Can I fix a boiler with no heating myself?
You can safely check the thermostat settings, timer, batteries, boiler pressure and whether radiator valves are open. Do not remove the boiler cover or attempt internal repairs, as boiler components should only be checked by a qualified heating engineer.
Why do I have hot water but no central heating?
On a combi boiler, this often points towards a diverter valve, control issue or circulation fault. On a system with a cylinder, it could be a zone valve or programmer issue. An engineer visit is the best way to confirm the fault without unnecessary parts being fitted.
What does the £50 diagnostic fee include?
The standard £50 diagnostic fee covers an engineer visit to inspect the issue. After diagnosis, the vetted subcontractor engineer provides a written fixed-price quote for any repair needed, so you know the cost before deciding whether to proceed.
Should I reset the boiler if the heating is not working?
If the manual suggests a reset and it is safe to do so, one reset is usually reasonable. If the boiler locks out again or still does not heat the radiators, stop resetting it and book a diagnostic visit.
Could cold radiators be caused by sludge?
Yes. Sludge and dirty heating water can restrict circulation and cause cold spots, slow warm-up, noisy operation or some radiators not heating at all. An engineer can check whether the problem is local to radiators or linked to wider system circulation.
Do KJ Plumbers cover my area in the North West?
KJ Plumbers helps customers across the North West by arranging vetted subcontractor engineers for boiler and heating faults. Share your postcode and the symptoms, and we will let you know the next available visit options.
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Photos, video and voice notes welcome. Vetted local engineers · no call-out fee · written quote before any repair.