If your boiler has been cutting out unexpectedly, you’re not alone. Many homeowners around Liss and the nearby GU35 areas, including Bordon and Alton, experience frequent shutdowns. One of the most common culprits is a faulty overheating sensor. In this guide, we’ll explain how the sensor works, why it fails, and what you can do to keep your heating running smoothly in Liss, Petersfield, Haslemere and beyond.
Recognising the Signs of Overheating
Your boiler has built-in safety features to prevent damage or risk of fire. The overheating sensor (sometimes called a thermal cut-out) is one of these. When it detects excessive temperatures, it triggers an automatic shutdown. Watch out for:
- Frequent, unexplained boiler cut-outs even when there’s demand for heat or hot water.
- Error codes on the boiler display, often indicating ‘overheat’ or specific fault codes like F22 or F28 depending on the brand.
- Unusually high temperature readings on the boiler pressure gauge.
- The boiler casing feeling hotter than normal before it cuts out.
Understanding the Overheating Sensor’s Role
Keeping You Safe
The overheating sensor is designed to switch off the boiler if internal temperatures rise above a safe limit. This can happen if water flow is restricted or if there’s a buildup of limescale or sludge in the heat exchanger.
How Sensor Faults Occur
Over time, sensors can become less responsive. Debris, limescale (common in hard-water areas like parts of Liss), or electrical wear can cause inaccurate readings. When the sensor thinks temperatures are too high, even if they’re not, it commands the boiler to shut down.
Why Liss Properties Are Prone to Sensor Issues
Homes in Liss and neighbouring Haslemere often face hard water challenges. Scale buildup reduces heat transfer efficiency, forcing the boiler to work harder and run hotter. Sludge from corroded radiators in older systems (common in Petersfield cottages) can block pipes and restrict flow, again triggering overheats. Regular maintenance is crucial in this environment.
Troubleshooting Your Boiler Shutdowns
Before you call out a Gas Safe engineer, try these simple checks in Liphook, Farnham or your own back boiler room:
- Check boiler pressure: Ensure it’s between 1 and 1.5 bar when cold. Low pressure can cause the boiler to overheat internally.
- Bleed radiators: Trapped air can restrict circulation and raise temperatures.
- Inspect external pipes and vents: Blockages can overheat the flue or ventilation pathways.
- Reset the boiler: Refer to your manual and clear the fault code. If it resets and then trips again, it’s likely an internal sensor issue.
When to Call a Gas Safe Engineer
If the boiler keeps shutting off after basic checks, you need professional help. A qualified Gas Safe engineer will:
- Test and replace the overheating sensor if necessary.
- Inspect the heat exchanger for scale and sludge.
- Perform a full boiler servicing to ensure safe, efficient operation all year round.
Preventing Future Overheating Faults
- Book an annual service: Regular servicing catches wear before it causes problems.
- Install a magnetic filter: Helps remove sludge for clearer water circulation.
- Consider chemical treatments: These reduce limescale in hard-water areas like Liss.
- Protect your investment: Look into our boiler cover for peace of mind against unexpected faults.
- If your boiler is nearing end of life, you might explore a new boiler installation for improved reliability and efficiency.
Frequently Asked Questions
What does the overheat sensor fault code mean?
It indicates the internal temperature sensor has detected temperatures above its limit. Often marked as F22 or F28 depending on the boiler make.
Can I replace the sensor myself?
No. The overheating sensor is part of the sealed hydraulic circuit and must be replaced by a Gas Safe engineer to ensure safety and compliance.
How much does sensor replacement cost?
Costs vary by model, but most Liss homeowners can expect a visit and replacement to range from £100 to £250, including parts and labour.
If you need help with your heating or boiler, our local engineers are here to help. Call us on (01420) 558993 or book online.
Written by Embassy Gas — your local heating experts covering Liss, Bordon, Alton, Petersfield and surrounding areas.