If there is no fault code but the boiler is still not working it means the sequence of operation the boiler follows hasn’t been disrupted.
This means that either the fault isn’t serious enough to be recognised by the boiler or the fault lies elsewhere.
Hot water problems with no fault code
Not enough water coming out of the tap.
For a combi boiler to produce hot water there has to be a demand. This means an amount of water has to be running through the boiler for it recognise the tap is running.
If a tap is broken or there is low water pressure in the property then the boiler will not recognise that hot water is required and won’t turn on.
A trickle of water coming from a tap isn’t enough to activate the boiler. Try a different hot tap in the property or all the hot taps at once if all the taps are slow.
Hot water is not hot enough
Combi boilers heat cold water up as it flows through the boiler. They are designed to lift the temperature of a set about of water by a set number of degrees.
If the water is flowing too fast through the boiler there isn’t enough time to heat it up. This cause the water temperature to stay too low.
Try to slow the flow rate of the water down by opening the tap less.
Plenty of pressure but no hot water
If there is plenty of water coming out of the tap but the boiler doesn’t recognise the demand there may be a fault with the boiler.
There is generally (but not always) a small turbine that spins in the flowing water. If this jams the boiler doesn’t know the tap is running.
This requires a gas safe engineer to investigate.
If you have had work done in your property recently on your hot and cold water pipes or your boiler there is a small chance the direction of flow could have been reversed.
The cold water has to come into the boiler though the cold pipe and exit through the hot pipe. If they are reversed the flow sensor won’t work.
Hot water cycles hot then cold
This is normally a blocked plate heat exchanger. The boiler tries to heat up the water then overheats because the plate heat exchanger is clogged with dirt. This causes the boiler to stop firing causing the water to go cold.
This cycle is repeated over and over again causing a cycling of hot and cold water.
You may need a gas safe engineer to replace or clean out the plate heat exchanger.
Heating problems with no fault code
No demand on the boiler – timer and thermostat off
If the timer and the stat aren’t turned on the boiler won’t come on. This is quite a common fault in spring and autumn. If the room temperature isn’t quite cool enough for the room thermostat to turn the heating but it still feels cool.
The easiest fix is to turn your thermostat up a bit higher.
No demand on the boiler – timer and thermostat on
This sounds like a problem with either the timer or the room thermostat. Try turning the thermostat up as high as it will go, generally around 30 degrees.
If this doesn’t work contact a heating engineer or electrician.
No demand on the boiler – more than one thermostat in the property.
If there is more than one room thermostat in the property it is highly likely there are zone valves controlling the heating in the different areas of the house.
In a system with zone valves the room thermostat controls the valve which in turn controls the boiler.
Contact a heating engineer of you are unsure as the wiring of zones can be complicated.
In general if the room stat and timer are sending power to the zone valve the little lever on the side of the zone valve will be loose (the lever is shown in the picture above). If it is stiff there is no demand.