Boiler Overheating? Here’s Why, And What You Can Do About It.

Having problems with your boiler overheating, and cutting out when your hot water is on? No problem.

In our 5-minute guide, we’ll cover everything you need to know, so you can get your boiler up and running again.

Rather invest your hard earned cash in a new and reliable boiler with a long warranty? You can get a Worcester boiler fitted by HEATABLE. Their clickable form takes less than 90 seconds to complete, and your price will be displayed on screen.

Why Does My Boiler Overheat, And Then Cut Out?

When your overheats and cuts out, it’s called a boiler lockout. This is a shutdown procedure that all manufacturers incorporate into their design.

So, when a boiler becomes unsafe, it shuts down.

The problem then needs to be fixed, and the boiler reset.

What Causes A Boiler To Overheat

#1 – Removing Pressure Release Valves

Pressure release valves are exactly that. When a boiler gets hot, it needs to relieve pressure through the PRV.

But, PRVs are known to leak. Some (dodgy) engineers will remove or seal the PRV to stop the leak, not realising that this can lead to a boiler overheating and worst-case; exploding!

#2 – Failed Thermistor

Thermistors will work in line with the boiler’s heart; the PCB. The thermistors let the PCB know if the demand for temperature (and therefore, gas, oil, or LPG) is more, or less, than it is currently.

A failed thermistor could result in too much fuel being provided, water getting very hot, and the boiler overheating.

#3 – Limescale On The Heat Exchanger

If you’ve read our guide to boiler noise, specifically, boilers making whistling and kettling noises, you’ll know it’s a problem related to the heat exchanger.

Limescale comes from mineral content in water. It happens in hard water areas. When it builds up on the heat exchanger, it creates hotspots.

These hotspots are what make the whistling sound, but it also means water is boiled at temperatures higher than it should be.

This leads to the internal components in a boiler overheating when the heating is on.

#4 – Blockages

There are two common blockages with heating systems:

  • Heating sludge blockages
  • Condensate pipe blockages

Heating Sludge

Central heating sludge is debris that comes from the inside of pipes, valves and radiators. Essentially, it’s dirty water with parts of rust in it.

When it clogs up a heating system it can create back pressure, sometimes blowing the pump seals. If the PRV isn’t fully functional, it can lead to a boiler overheating and turning off.

Condensate Blockages

A condensate pipe vents gas from your boiler outside.

If your boiler is overheating in the winter or in the morning, there’s a good chance this pipe is frozen.

And, if your boiler is overheating throughout the year, there’s a good chance leaves and dirt have made their way into the condensate pipe.

#5 – Pump Overheating

One problem that’s overlooked when it comes to overheating boilers, is the pump.

When pumps are overheating, there’s usually one reason; it’s seized.

Pumps should be warm, as they are motorised, but they shouldn’t be hot. If a pump is too hot to touch, there’s a good chance that internal components are seized.

A gentle tap can sometimes stop a seizure, but it doesn’t fix the problem. The pump needs to be taken apart, cleaned and inspected.

What You Can Do To Prevent Your Boiler Overheating

The most common causes of boilers overheating is limescale and sludge build up. Preventing boiler lockouts from overheating is simple.

  1. Hot flush your boiler to remove limescale and heating sludge
  2. Add central heating inhibitor to your heating system
  3. Install a scale reducer
  4. Install a magnetic system filter.

What’s Next?

Hopefully that’s helped uncover the reason why your boiler is overheating and cutting out. Still no good? Check out our guide to top combi boiler problems here.

Prefer a boiler replacement? Get your on-screen price in less than 2 minutes.

Avoid Expensive Breakdown Costs
Boiler Replacement Promise: If it's under 7 years old and we can’t repair it, we’ll replace it.
Try YourRepair. From £9/mo
All plans include: annual boiler service, all parts and labour, unlimited support and 24hr helpline.
  1. Hi, I have Ariston Microgenus 23. Heating works fine,but hot water not. It heats up to maximum and cut off for 12 seconds and fire it up again for 12 seconds and again and again. Looks for me like overheating and after cool down and switch on again. What could be the reason?

Leave a comment

Your email address will not be published. Required fields are marked *


Fix things and tutorials

Get a Boiler on Finance

The best pay monthly packages available

Read guide
Heatable Boiler Replacement

Want a new boiler from HEATABLE?

Read guide
WarmZilla Boiler Replacement

Want a new boiler from WARMZILLA?

Read guide
Boiler Installation Costs

Confused about new boilers and their costs?

Read guide