A boiler overheating is a serious issue that can cause damage to your heating system, increase energy bills, and even pose safety risks. If your boiler is overheating, you may notice strange noises, leaking water, or even automatic shutdowns. Here’s what causes boiler overheating, how to fix it, and when to call a professional.
🔥 Why Is My Boiler Overheating? Common Causes
1️⃣ Limescale Buildup (Kettling)
- Hard water causes limescale deposits in the heat exchanger, leading to poor heat transfer and overheating.
- Symptoms: Rumbling or kettling noises, reduced efficiency.
2️⃣ Blocked or Faulty Pump
- If the pump is blocked or not working properly, hot water cannot circulate, causing overheating.
- Symptoms: Radiators stay cold, unusual boiler noises.
3️⃣ Low or No Water Flow (Airlocks or Closed Valves)
- A lack of water circulation due to airlocks or closed valves can cause the boiler to heat up excessively.
- Symptoms: Overheating warnings, gurgling sounds, no hot water.
4️⃣ Faulty Thermostat or Temperature Sensor
- If the thermostat fails to regulate temperature, the boiler can overheat.
- Symptoms: Water gets too hot, inconsistent heating.
5️⃣ Blocked Heat Exchanger
- A clogged or damaged heat exchanger prevents heat dissipation, leading to overheating.
- Symptoms: Sudden boiler shutdowns, high-pressure readings.
6️⃣ Faulty Pressure Relief Valve (PRV)
- This valve releases excess pressure. If it’s blocked or broken, pressure can build up, causing overheating.
- Symptoms: Leaking water, rising pressure levels.
🛠 How to Fix an Overheating Boiler
⚠ Important: If your boiler is overheating, turn it off immediately to prevent damage or danger.
Step-by-Step Troubleshooting:
✅ 1. Check the Boiler Pressure
- Ideal boiler pressure is 1.0 – 1.5 bar.
- If the pressure is too high, release excess water from the radiator valve.
✅ 2. Bleed the Radiators
- If airlocks are causing water flow issues, bleed the radiators to remove trapped air.
✅ 3. Inspect the Thermostat
- Test if the thermostat is regulating temperature correctly. If faulty, replace it.
✅ 4. Flush the System (Descale the Heat Exchanger)
- If limescale buildup is the problem, a power flush or chemical flush will remove deposits.
✅ 5. Check the Pump for Blockages
- If the pump is blocked or failing, it may need cleaning or replacement.
✅ 6. Inspect & Replace Faulty Valves
- Ensure all valves are open and functioning properly.
Now, Consult with an Engineer
🛑 When to Call a Professional Boiler Engineer?
🚨 Call a Gas Safe Engineer if:
✔ The boiler keeps overheating after troubleshooting.
✔ There are leaks, unusual smells, or carbon monoxide alarms sounding.
✔ You suspect a faulty heat exchanger or pressure relief valve.
✔ You need a professional power flush for limescale buildup.
At A&C Heating and Plumbing Ltd., our Gas Safe registered engineers provide fast and reliable boiler repair services to fix overheating issues safely.
What Are the Causes of An Overheating Boiler?
Build-up of limescale
Limescale accumulation on the heat exchanger restricts water flow, leading to overheating. This phenomenon, known as “kettling,” can produce kettle-like whistling sounds.
If you notice such sounds, it is advisable to contact a heating engineer to flush out the system and eliminate limescale. Addressing this issue promptly not only prevents overheating but also extends the lifespan of your boiler.
Blockage in the system
Unusual sounds from your central heating system or radiators that fail to heat up properly are indications of a blockage. Surplus air in the radiator can be discharged by bleeding it.
In cases of severe blockages, a heating engineer should perform a power flush, a thorough cleansing process that removes limescale, rust, and debris. A power flush restores proper water circulation, allowing efficient heating throughout the space.
Fault with the pump
The pump plays a vital role in circulating water within the central heating system. A malfunctioning pump prevents hot water from leaving the boiler, potentially causing overheating.
While a heating engineer might attempt to repair the pump, it is often necessary to replace it entirely to restore proper functionality.
Thermistor issue
The thermistor monitors water temperature, enabling the PCB to adjust the temperature based on demand. A failed thermistor can result in excessively high-water temperature, leading to boiler overheating.
However, you must remember that only a qualified heating engineer should work on a thermistor, and it will likely require replacement to rectify the issue.
How to Tackle the Overheating Problem?
When it comes to rectifying an overheating boiler, the approach to fixing the issue depends on the underlying problem. It is essential to employ the services of a certified specialist for any of the common causes I have mentioned above.
Ensuring the employment of a fully qualified engineer is vital for boiler installation, repairs, and servicing. Engaging an individual lacking the necessary qualifications could exacerbate the overheating issue and potentially lead to more severe consequences.
Future Tips to Stop Overheating Before It Happens
Suppose you have resolved the issue by hiring an expert engineer. In such a case, it’s time to take care of it to avoid overheating from happening again in the future. Well, you can carry out several proactive actions to ensure its avoidance.
Regular Servicing
It is highly recommended to schedule regular boiler servicing. This crucial maintenance practice helps prevent dangerous issues such as overheating. Qualified engineers possess the expertise to identify and address any potential problems before they escalate, ensuring the safe and efficient operation of the unit.
Prompt Repairs
In case any repairs are necessary, it is crucial to rely on professional engineers to promptly address them. Timely repairs can prevent situations where a boiler becomes unsafe and prone to shut down or overheating.
Upgrading Old Boilers
Consider replacing old boilers with newer models. Modern boilers come equipped with advanced safety features designed to mitigate the risks associated with overheating. By investing in a newer unit, you can enhance the overall safety and efficiency of your boiler system.