Your guide to dealing with common heating problems

If your boiler doesn't come on when you expect it to, please run through the following check list before reporting to SLH.

Close-up of a circular green switch on a yellow panel, labeled 'ON' at the top with a line symbol and 'OFF' at the bottom with a circle symbol.

1. Is the electrical power switch on the wall switched on?

(white ON/OFF switch next to boiler)

Close-up of a lit gas stove burner with blue flames, black metal grate, and white hexagonal tile background.

2. Have you got gas and is there credit on the meter?

If you have any other gas appliances, are they working e.g. cooker, gas fire?

Person pointing at the control panel of a white appliance, possibly a boiler, while holding a tablet.

3. Some boilers have a small RESET button on the front panel.

If the boiler does not come on try pressing this button and holding in for 5 seconds.

Close-up of a digital thermostat showing "Heat Setting 68°," "Inside 70°," and the time 9:25 AM, with options for System Heat, Fan Auto, and Schedule.

4. Check the room thermostat, usually fitted in the hall.

Turn it up fully to check that the boiler comes on. Then reset it to the temperature you prefer, normally between 21 and 23 degrees.

A hand adjusting a circular mechanical timer switch with numbered time intervals around the dial, used for setting on/off times for electrical devices.

5. Is the programmer in timed mode?

Switch to ‘CONSTANT’ to check the boiler comes on, then reset to timed mode. Check the time of the clock. If your electricity has been off for any length of time it is likely that the clock is showing the wrong time. Reset the clock if necessary.

Hand resting on a white radiator with an adjustable thermostat knob on the side.

6. Are the radiators warming up?

Turn the radiator valves to the side of each radiator fully up and down a couple of times to ensure the valve is working freely. To test the radiator please turn each valve to the highest number. After testing, reset to your original required setting.

Still experiencing a fault?

If there is still a fault on the system please report the issue using mySLH or call us on 0330 303 3000.

Person using a tablet while pointing at the control panel of a wall-mounted boiler or heating system, possibly for repairs or adjustments.

Central heating boiler guides

Here are the user guides for the main types of boilers that we fit in our homes. Please check the model of your boiler and select the correct user guide below. 

Reduce your flow temperature and save ££s

Did you know that, if you’ve got a condensing combi boiler, you can save money and make your heating system more efficient by reducing the flow temperature on your boiler?

As standard, most boiler manufacturers set their boiler flow temperature at 80 degrees, but in most well-insulated homes you can drop that temperature to 60 degrees and increase your boiler’s efficiency from around 75 to up to 95% without affecting the comfort of your home, saving you money and helping the environment too.

How to adjust your boiler flow temperature

The procedure for adjusting your boiler flow temperature will vary from appliance to appliance but the information below is a general guide. For specific instructions for your boiler, check out the user guides for our commonly-installed boilers on this page.

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large dark blue number '1' is visible to the right

Find the panel on your boiler and navigate to the menu that controls the temperature of your heating system flow (not your hot water temperature – this is separately controlled)

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large number '2' is visible to the right

Adjust the flow temperature down to 60 degrees Celsius – you might do this with arrow buttons depending on your model.

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large number '3' is visible to the right

Once you’ve reached 60 degrees Celsius you may need to confirm the setting, depending on your model.

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large number '4' is visible to the right

That’s it! You may find that your radiators take longer to warm up than before and the heating may stay on longer to achieve your desired room temperature. However, because you’re heating the water in your system to a lower temperature, it will still be more efficient than before.

Step 1

Find the panel on your boiler and navigate to the menu that controls the temperature of your heating system flow (not your hot water temperature – this is separately controlled)

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large dark blue number '1' is visible to the right
Step 2

Adjust the flow temperature down to 60 degrees Celsius – you might do this with arrow buttons depending on your model.

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large number '2' is visible to the right
Step 3

Once you’ve reached 60 degrees Celsius you may need to confirm the setting, depending on your model.

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large number '3' is visible to the right
Step 4

That’s it! You may find that your radiators take longer to warm up than before and the heating may stay on longer to achieve your desired room temperature. However, because you’re heating the water in your system to a lower temperature, it will still be more efficient than before.

"White tankless water heater mounted on a blue wall, displaying '55' in red digital text, with two control knobs on the front panel and a vent pipe at the top. A large number '4' is visible to the right

How to repressurise your boiler

Low pressure in your central heating system occurs for several reasons. It will happen when you bleed your radiators or when there is a leak in the system. If you bleed your radiators, you will need to top up your pressure to 1.5bar as described below. If your system continues to lose pressure following the top up, chances are you’ve got a leak, so give us a call to investigate.

  • First, check the pressure on your boiler. Different boilers have different pressure gauges so check the user guide for your boiler below to find yours.
  • Pressure is measured in bars. If your pressure is below 1bar then it’s time to top it up.
  • Switch off your boiler and allow it to cool down
  • Find the fill loop attached underneath your boiler. It will be a u-shaped flexible hose with taps at either end.
  • Open the taps and you will hear water entering the heating system. Wait until the pressure reaches 1.5bar.
  • Switch the boiler back on to check if it fires up. You may need to press the RESET button.
  • If the boiler doesn’t fire up, then there may be another problem. Follow our six-point checklist above and if you’re still struggling call us on 0330 303 3000 and we will arrange for a gas engineer to come and investigate.