A Glow-worm boiler that keeps turning off when the set temperature is reached is normal. But in some cases, a boiler switching itself off and on frequently indicates a problem. And there are a few reasons for that. Most of these will need to be looked at by a professional. Here, we look at what a normal on and off timeframe is and what isn’t.
Glow-worm boiler keeps turning off
A glow-worm boiler that keeps shutting off after a few minutes is most likely due to the boiler short cycling where it turns on to reach the set temperature then switches off once its reached. Other causes are a faulty thermostat or a lack of water flow.
Causes of a Glow worm boiler turning itself off
- Lack of water flow.
- Boiler short cycling.
- Faulty thermostat.
- Oversized boiler.
- High boiler pressure.
- Low water pressure.
- Faulty pressure relief valve.
Glow worm boiler troubleshooting
Is your Glow-worm boiler malfunctioning? Try basic troubleshooting before calling an engineer:
- Check the pilot light – Relight if extinguished
- Examine the burner and flue for blockages
- Ensure the gas valve is open fully
- Reset any tripped safety switches
- Check the system pressure gauge and refill water if low
- Bleed radiators to remove trapped air
- Clean the condensate pipe if blocked
| Issue | Troubleshooting Tips |
|---|---|
| Pilot light out | Relight pilot |
| Burner/flue blocked | Clear obstructions |
| Gas valve closed | Open valve fully |
| Safety switches tripped | Reset switches |
Lack of water flow
A closed valve somewhere on the system, or trapped air will restrict the water flow to the boiler. If the water flow isn’t sufficient, the boiler will turn off. Check the stop tap and also the radiator valves to ensure the ones that need to open, are fully open. If too few are open, the boiler can overheat. Blocked pipes could also slow down the water flow.
Boiler fires up randomly
The preheat function, when turned on, provides you with hot water quickly when turning on the hot tap. The boiler keeps the part of the boiler that heats tap water – the plate heat exchanger, hot so it’s ready to send hot water to the tap when needed. The boiler fires up for short periods to keep this part warm.
We can tell the preheat function is activated when looking at the display flashing independently without a demand. It is useful if the hot taps are turned on frequently but if the house is mostly empty during the working week, it doesn’t need to be on.
This preheat function can be deactivated by the user and doesn’t need an engineer to come and sort. On Glow worm boilers, this preheat function is manually activated and deactivated by using the ECO button on the front of the boiler. If unsure, ask the installer or check the user manual for the boiler.
Boiler short cycling
If your Glow worm boiler keeps on firing up and then turns off again quickly, it may be short cycling. A short cycling boiler is when the burner inside turns on and off quickly, within a minute. This means whenever heating demand is needed, like when the radiators come on, it is quickly met before the boiler shuts down again, then restarts shortly after. It can happen for a few reasons but the main one being an oversized boiler.
In this case, you may notice your heating bills becoming more expensive as well as it leading to the boiler getting more wear and tear over time, resulting in increased repairs.
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Oversized boiler
It is important to get the right size boiler for your property and the number of occupants. A boiler that’s too powerful heats up too quickly and then shuts off again quickly then turns back on as the room temperature room has not been met. It repeats this cycle frequently instead of heating up and running slowly.
Faulty thermostat
A faulty thermostat that isn’t sensing the correct temperature of the water will shut itself off to prevent the boiler from overheating. A faulty thermostat may think the desired temperature has been reached and send a message to switch off the heating. A replacement thermostat should solve the issue.
Internally, a faulty overheat thermostat can also cause the boiler to switch off. This thermostat is crucial to the safe performance of the appliance because, without it, the boiler can carry on getting hotter and eventually catch fire. But if it’s faulty it could make the appliance turn off earlier than it should – before the desired temperature has been reached.
High boiler pressure
If the water pressure is too high on the gauge, there could too much air in the system so the boiler is shutting down for safety reasons. Too much air in the system can reduce the water circulation so the required temperature is never reached, but the water temperature is very hot.
Check the pressure on the gauge isn’t too much above 1 bar, if it is, you will need to bleed a radiator until it comes down to around that level.
Low water pressure
This is a common cause of the Glow worm boiler turning off, but this is true for all boiler makes. When the water pressure gets too low, the boiler will turn itself off. If there is a leak in the system and the heating or hot water is turned on, the boiler may work for a while before the water pressure drops enough to cause it to stop the boiler working.
Faulty pressure relief valve
If boiler pressure isn’t the problem, but the boiler keeps switching off, a faulty pressure relief valve may be the culprit. The prv works to shut the boiler down in cases where the pressure is too high, after3 bar. If the prv is faulty (usually because debris gets stuck), it may send a message for the boiler to switch off.
Glow worm boiler reset button
A Glow-worm boiler reset button is used to reset tripped safety switches and resume operation after a fault causes shutdown.
Steps to reset a Glow-worm boiler:
- Locate the reset button on the boiler body
- Press and hold the reset button for 5-10 seconds
- The boiler will make a noise as it resets
- The pilot should automatically relight
If the boiler does not restart, the fault may reoccur quickly. Contact an engineer to inspect the boiler and fix the underlying issue.
Frequent resetting indicates a problem needing repair. Don’t just keep resetting an underperforming boiler.
Annual servicing can help minimize reset requirements by catching problems early.
Refer to your Glow-worm boiler user manual for key information like:
- Initial setup, programming, and operation
- Diagnosing error codes
- Locating the reset button
- Basic maintenance procedures
- Troubleshooting tips
- Model specifications and repair parts
- Warranty and service contact details
Keep the physical manual or PDF accessible to use as an ongoing reference.
glow worm boiler problems no hot water
If your Glow-worm boiler provides heating but no hot water, potential causes include:
- Faulty hot water program settings
- Failed diverter valve
- Leak in the heat exchanger
- Blocked/damaged condensate pipe
- Circulation pump failure
- Stuck motorised valve
Try basic troubleshooting first. If the no hot water issue persists, contact a Gas Safe registered engineer to service the boiler and properly diagnose the problem. Repairs may be needed.
Combi boiler hot water goes cold
A common problem with combi boilers is hot water goes cold before getting hot again when showering. One reason is a sudden increase in demand when someone in the house turns a hot tap on. This puts extra demand on the combi to supply both outlets at the same time. Another reason could be an internal problem like a blocked heat exchanger, especially on old boilers.
If you feel it’s time for a new boiler, check out BoilerCentral.com which has a wide range of boilers at a great price including installation and very long warranties: Click here to see why we recommend them.
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*The information in this article should be used for general guidance only and not as financial advice. Full details are on the link in the footer to our disclaimer page. Always discuss your requirements with a competent and suitably qualified professional before undertaking any work.