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Error 101 · 104 · Gas boilers
Errors 101 and 104: the boiler overheats or the water isn't circulating
The boiler has stopped because the water has got too hot (101) or because it isn't circulating properly (103 to 107; the most common is 104). The two usually have the same cause.
What it means
To heat safely, the water has to circulate through the boiler and the system. If too little water circulates, the temperature can rise faster than normal: the boiler detects this and stops with a code from 103 to 107.
If it still gets hotter than it should, it shows 101, which is a safety lockout due to overheating.
Most likely causes
- Closed valves: the ones under the boiler, or lots of radiators turned off at the same time.
- Air in the circuit, for example after topping up or after building work.
- Low pressure in the heating system.
- Dirt build-up in the system or in the heat exchanger.
- The circulation pump or a temperature sensor.
What you can check yourself
Without tools and without opening the unit.
- Check the valves under the boiler: with the handle in line with the pipe, they're open.
- Open up any radiators you've turned off: if lots of them are off, the water has very few places to circulate.
- Check the pressure gauge with the heating cold: it usually reads between 1 and 1.5 bar. If it reads lower, see the page on error 108 or 1P4.
- Reset it once if the boiler has locked out.
If it stops again after two or three resets, don't keep trying: a temperature lockout that keeps happening needs to be checked. Book an engineer.
If the water heater, boiler or heat pump is leaking a lot of water: turn off the main water stopcock in your home and call us on 871 559 176. That stops the leak and saves you from water damage.
If you smell gas: turn off the gas at the shut-off valve and open the windows. Don't touch any switches or plugs, and call us from outside the property.
If the unit is smoking or getting hotter than it should: switch it off, disconnect it from the mains and call us.
If we come out
What we check and how to stop it happening again
What the engineer usually checks
- Bleeding the circuit and working pressure
- Circulation pump
- Flow and return temperature sensors
- Condition of the heat exchanger and the system
How to catch it early
Air and dirt in the circuit get worse over the years. At the service, the pressure, the pump and the sensors are checked before any of this gets to the point of stopping the boiler.
See the maintenance plansStill not sorted?
Book an engineer and give us the code and the model of your unit. That way we know what to bring.