❄️ Boiler Not Heating? Quick Fixes

No hot water or central heating is miserable, especially in winter. Before you assume your boiler is broken, try these quick checks. Many heating problems have simple solutions that take minutes to fix.

1. Check the Boiler Display

What to look for:

1. Is the boiler switched on? Check the on/off button and power indicator
2. Is there an error code displayed? (e.g., F1, F28, A00, E1)
3. Take a photo of any error code - your engineer will need it
4. If display is blank, check the power switch and circuit breaker

Error codes tell you what's wrong. Google your boiler make + error code for quick diagnostics.

2. Check the Pressure Gauge

Low pressure is the #1 reason boilers stop heating.

What you need to do:

1. Locate the pressure gauge on your boiler (dial with numbers, usually 0–3 bar)
2. It should read between 1 and 2 bar when cold
3. If it's below 1: Pressure is too low and heating won't work

How to restore pressure:

1. Find the filling loop - a small lever or valve under or near the boiler
2. Slowly open it (turn anticlockwise) - you'll hear water rushing in
3. Watch the pressure gauge rise to about 1.5 bar
4. Close the filling loop when pressure reaches 1.5
5. Wait 10 minutes, then test your heating

3. Check the Thermostat

• Is it switched on?
• Is the temperature set higher than room temperature?
• Try setting it 5°C higher and wait 5 minutes
• If it's a smart thermostat, check the battery level
• Is the thermostat away from cold walls or drafts that might make it think the room is colder?

4. Bleed the System

Air in the heating pipes stops heat circulating. This is called "bleeding the radiators."

Quick bleed check:

1. Feel the radiators - are they hot at the bottom but cold at the top?
2. If yes, they need bleeding
3. Use a radiator bleed key (turn the small square valve on the radiator) to release air
4. Open slightly until water starts to drip, then close immediately

See our "How to Bleed a Radiator" guide for detailed steps.

5. Reset the Boiler

1. Turn off the boiler at the control panel
2. Wait 30 seconds
3. Turn it back on
4. Listen for a clicking/whooshing sound - this is the ignition
5. Wait 2 minutes for the system to stabilize

If the boiler doesn't make an ignition sound, the burner isn't firing - you'll need an engineer.

6. Check for Frozen Pipes

In winter, pipes outside or in unheated spaces can freeze, blocking water flow.

Signs of freezing:

• No water coming from taps (besides hot water from the boiler)
• Visible frost or ice on external pipes
• Strange gurgling sounds in pipes

How to thaw:

• Use a heat gun or hot water bottle on the frozen section
• Never use a blowtorch or open flame - risk of fire
• Prevent future freezing by insulating pipes with foam lagging

When to Call an Engineer

• Pressure won't stay above 1 bar (indicates a leak)
• Boiler displays an error code that doesn't clear
• Boiler won't ignite (no clicking or whooshing sound)
• Radiators are hot but no hot water, or vice versa
• You smell gas or burning
• None of the above checks fix the problem

Information to Have Ready

• Boiler make and model
• Any error codes
• Pressure gauge reading
• Age of the boiler (when installed?)
• When was it last serviced?
• What's not working - heating, hot water, or both?

Why Boilers Lose Heat Over Time

Sludge and debris naturally build up inside a central heating system over years of use, settling in radiators and pipework and reducing how effectively heat circulates around the house. This is one of the most common reasons a boiler seems to be working but the home isn't heating properly.

Air trapped in the system has a similar effect, preventing hot water reaching parts of the system and showing up as cold radiators or patchy heating even when the boiler itself is firing correctly.

Preventing Future Heating Problems

An annual service catches sludge build-up, pressure issues and early component wear before they affect how well your home heats. A power flush every few years clears out debris that's already built up in an older system.

Bleeding radiators regularly, particularly at the start of the heating season, prevents trapped air causing cold spots and keeps the whole system working as it should.

Common Mistakes When Diagnosing the Fault

Repeatedly resetting the boiler without identifying why it's cutting out can mask a fault that gets worse over time - if a reset doesn't hold, it's better to get it looked at than keep resetting it.

Assuming the boiler itself is faulty when the real issue is trapped air or sludge in the radiators is a common mistake - bleeding radiators first can save an unnecessary call-out for what turns out to be a simple fix.

When It's More Than Just Heating

If you've lost hot water as well as heating, this points to a different class of fault, often related to the diverter valve or the boiler's primary heat exchanger, rather than a simple pressure or air issue.

Persistent heating faults on an older boiler are sometimes a sign the unit is nearing the end of its life - we'll always give you an honest view on repair versus replacement rather than just fixing the immediate symptom.

The Role of Thermostatic Radiator Valves

Thermostatic radiator valves (TRVs) let you control the temperature of individual rooms, but a stuck or faulty TRV can leave a radiator permanently cold or permanently on, regardless of what the room thermostat says. This is often mistaken for a boiler fault when the actual problem is a single valve.

If one specific radiator isn't heating while the rest of the house is fine, check the TRV first - it's a common, inexpensive fix, and far more likely than a fault with the boiler itself given the rest of the system is working normally.

Diverter Valve Faults Explained

Combi boilers use a diverter valve to switch between heating the central heating system and heating hot water on demand, and a stuck or faulty diverter valve can leave you with hot water but no heating, or the reverse, even though everything else about the boiler seems fine.

This is a more involved repair than a simple pressure or air issue, but it's a well-understood, common fault on combi boilers rather than a sign of a wider problem with the unit.

Quick Questions

Why does my boiler show hot water but no heating? This often points to a diverter valve fault or a heating-specific issue like trapped air or a stuck zone valve, rather than a fault with the boiler's core components.

Is it safe to keep resetting the boiler? Resetting once is fine, but if the fault returns immediately, stop and call an engineer rather than repeatedly resetting, which can mask a developing problem.

A boiler that's not heating properly is one of the most common calls we get, and in the majority of cases it's a straightforward, well-understood fault rather than anything serious. Working through the basic checks first can save you an unnecessary call-out, but if in doubt, it's always better to get it looked at than to keep living with a cold house.

If you've worked through the basic checks and your boiler still isn't heating properly, give us a call - we'll talk through what you've already tried and get an engineer to you as quickly as we can.

Key Takeaways

• Low pressure is the most common heating issue - check and refill via the filling loop
• Thermostats must be set higher than room temperature and switched on
• Air in radiators stops heating - bleed them if they're cold at the top
• Frozen pipes can block water flow in winter - thaw gently with heat
• If your boiler won't ignite or shows persistent error codes, call a professional