Why Is My Heating Not Working? A Troubleshooting Guide

Start Here: Is It Just Heating, or Hot Water Too?

The first step in diagnosing a heating problem is to check whether the issue affects just the heating, just the hot water, or both. This narrows down the fault significantly.

**No heating, but hot water works:** Likely a zone valve, programmer, or room thermostat issue

**No hot water, but heating works:** Likely a hot water zone valve or cylinder thermostat issue (system boilers); or a diverter valve fault (combi boilers)

**No heating AND no hot water:** Boiler fault, gas supply issue, or power problem

Step-by-Step Troubleshooting

Step 1: Check the Boiler Display

Does the boiler display an error or fault code? Look this up in your boiler manual or search online using your boiler model and the code number. Many faults are self-explanatory once identified.

Step 2: Check Gas Supply

Is the gas supply working? Test by turning on a gas hob. If there's no gas, check whether other neighbours are affected and call your gas supplier or National Gas Emergency (0800 111 999).

Step 3: Check the Power Supply

Is the boiler powered? Check the boiler's isolation switch (usually nearby), your consumer unit for tripped breakers, and that the timer/programmer is on.

Step 4: Check Boiler Pressure

The pressure gauge should read 1–1.5 bar when cold. Below 1 bar, repressurise using the filling loop. Above 2.5 bar, call an engineer.

Step 5: Check the Thermostat

Is the thermostat calling for heat? Set it above the current room temperature and check whether the boiler responds.

Step 6: Check the Timer/Programmer

Is the programmer set correctly? Check it's set to the right time and day and that a heating period is scheduled.

Step 7: Check Individual Radiators

Feel all radiators — if some are hot and some cold, the boiler is working but there's a distribution issue (see our radiator troubleshooting guide).

Step 8: Try a Boiler Reset

Many boiler faults clear with a simple reset (hold the reset button for 3–5 seconds). Allow 10 minutes after resetting before checking whether the fault returns.

When to Call an Engineer

If you can't identify or resolve the issue after these steps, or if you see any of the following, call a professional:

Gas smell

CO alarm sounding

Fault code that won't clear

Boiler making unusual noises

Visible leaks

Halo Heating offers 24/7 emergency cover across West Sussex. Call us and we'll get an engineer to you promptly.