Why is my heating coming on at random times?

Author: Florence Bergstrom  |  Last update: Thursday, February 19, 2026

Check the room thermostat settings and make sure that it isn't programmed to turn the heating on when we don't need it. In more modern systems, this will likely be caused by a faulty solenoid valve always remaining open on the heating side.

Why is my heating turning on by itself?

It could be a component, such as the heat exchanger or an internal thermostat, in which case you should not attempt to fix it – call a gas engineer who will be able to assess the situation and recommend a repair or replacement. Making sure your boiler has its annual service should prevent this stop-start pattern.

Why is my heating coming on when not scheduled?

There are two main reasons that your heating is on when it should be off. It normally comes down to a problem with either your diverter valve or your check valve. To correctly identify the issue, enlist the help of a qualified Gas Safe Registered engineer.

Why has my heating come on when it's off?

The reason your radiators heat up - even with the heating off - is because the valve doesn't close off the heating side of it fully. This means water can still pump around the radiators when the heating should be off. There's not much you can do when a mid position / 3 port valve does this, except to change it.

Why is my heating coming on in the middle of the night?

The most common cause is a faulty thermostat that sends incorrect signals, causing the boiler to fire up when it shouldn't. Other factors can include issues with the boiler's internal components, such as the pump or valves, which may not be working correctly.

Is It Better To Leave The Heating On Constantly? Boilers & Heat Pumps | Consumer Advice

How do I stop my heating coming on at night?

Thermostat. You can set your thermostat to its minimum temperature before you go to bed in the evening. If you want to be sure the heating doesn't come on, set the temperature as low as it will go, and it's unlikely the heating will come on unless the temperature in your house falls dramatically.

What are the symptoms of a faulty diverter valve?

Symptoms of a faulty diverter valve often include inconsistent hot water flow and radiators not heating properly. Homeowners may notice that radiators remain cold even when the boiler is on. Inconsistent water temperatures are common, with water switching from hot to lukewarm or cold unexpectedly.

Why would heat be on when thermostat is off?

If the anti gravity valve is broken or blocked and is not doing its job of stopping the natural convection process, it means heat will rise through your central heating system. Your radiators will be on, even though your thermostat is off.

How to stop heating from coming on automatically?

Turning off modern boilers is simple; simply locate the power switch and turn it off. In addition, you can often shut off the heating and hot water separately. You can also turn the thermostat down, or turn it all the way to zero to prevent the boiler from heating.

Why does my heater go on and off randomly?

A furnace cycling on and off repeatedly can be caused by various reasons, from dirty filters and obstructions in ducts and registers to incorrect thermostat settings and faulty limit switches. By following the steps above, you can help prevent your furnace from cycling too frequently and save energy costs.

Why does heat keep kicking on?

Change Thermostat Batteries

Your thermostat may not read temperatures indoors correctly, and trigger the heating system to start and then stop too soon. Check the thermostat batteries replace them with fresh ones and see if this stops the short cycling.

Why do I keep randomly heating up?

Feeling hot can be a natural symptom of menopause or a reaction to something you ate or drank. It can also be due to an underlying health condition, such as an issue with your thyroid gland. (Hyperthyroidism, when you have too much thyroid hormone, speeds up your body's processes.

Why does my heating come on before the set time?

The most common reason for the heating coming on when you don't expect it is due a mis-understanding on comfort level programming. Heatmiser Thermostats don't use on/off times, they use Comfort Levels. Rather that turning your heating on and off, comfort levels let you program different temperatures throughout the day.

Why is my heating coming on when not scheduled but?

Check the room thermostat settings and make sure that it isn't programmed to turn the heating on when we don't need it. If it's not that, then there are two other potential issues: it could be a faulty mechanical valve or it could be what is known as reverse flow.

Why does my heater randomly turn on?

A furnace can come on by itself as part of its regular operation to maintain the temperature in the home. If the furnace turns on erratically or when the control panel is turned off, there may be a fault with the furnace or the controlling thermostat. This requires maintenance by a technician.

Why does my furnace keep turning on and off without heating?

If your furnace keeps turning off and on, your thermostat may be the culprit. A malfunctioning or improperly placed thermostat can cause your furnace to short cycle. Common issues include: Old wiring or dead batteries: Replace batteries or old wiring to ensure accurate temperature readings.

Why would my heating come on on its own?

If your system is operating outside this automated procedure then it is possible that the any one of the following has failed in some way: Thermostat not reading correctly. Wiring from thermostat to heat system is damaged. Relay and control board on heat system has failed or gone intermittent.

Why is my heating coming on when it's switched off?

If your home radiators will not switch off even when the central heating isn't on, the most likely cause of the issue is troubles with a diverter or check valve. Should the valves become damaged or blocked, they can continue to transport hot water to your radiators even when the thermostat is switched off.

Why is my heat constantly running on auto?

If the thermostat isn't the issue, it may be the heating unit itself. The primary controller dictates when the unit turns on and off. If it's not working properly, it can no longer control this, and your heater may run continuously. Your primary controller will need to be replaced by a professional.

How do I stop my heating from coming on?

If your thermostat does not have an off switch, you can turn the temperature below the current room temperature. You will want to do this by several degrees. If your heating system and thermostat are working, it should turn off. If the system does not turn off, it is time to turn off the power.

How to tell if a thermostat is bad?

A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.

Why is my heater running when turned off?

The wiring, switches, or heating sensors can fail on your unit. If this is the case, then you'll need to replace the thermostat with a newer model. A damaged primary controller can also cause the furnace to stay turned on. This is the main heating element of the system.

How do I know if my diverter valve is stuck?

Signs a diverter valve is stuck

If your diverter valve is sticking, you'll soon know about it. Whether that's standing under a cold shower because you've got no hot water or facing a chilly evening because your radiators won't switch on. Other things to look out for include: No hot water from the taps.

How much does it cost for a plumber to replace a diverter valve?

$100 – $350 shower cartridge replacement cost

Plumbers charge $100 to $300 in labor alone to replace a shower mixing valve or diverter valve.

Where is the diverter valve located?

If you have a showerhead over your bath, the diverter allows you to choose whether you want the water to come out of your bath taps or out of the shower head. It's usually a lever that's situated behind the bath taps that you can pull up or push down. System and conventional boilers don't require a diverter valve.

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