Which system have you got?
The checks depend on how your hot water is made. If there is no hot water cylinder in the house, you have a combi: the boiler heats water the moment you open a tap. If there is a cylinder, usually in an airing cupboard, the boiler heats the cylinder on a timer and the taps draw from it.
The two fail in different ways, so find the cylinder, or confirm there isn't one, before you do anything else.
On a combi
Check the pressure
If the gauge reads under 1 bar the boiler may be locked out for that reason rather than a hot water fault. Top it up and try again.
Check the display
A fault code narrows it down a lot. Note it before you press reset, and only reset once.
Run a hot tap fully
Some combis need a decent flow before they fire. A tap barely open, or a blocked aerator, may not trigger it.
Is it lukewarm or cold?
Stone cold means the boiler isn't firing for hot water at all. Lukewarm, or hot then cold, points at scale in the heat exchanger or a flow problem.
- Diverter valveThe part that sends the boiler's heat to either the radiators or the hot water. When it sticks, you get one or the other. The most common cause of heating but no hot water on a combi.
- Hot water sensor or flow switchTells the boiler you have opened a tap. If it fails, the boiler never knows to fire.
- Plate heat exchangerWhere the heat passes into the tap water. In hard water areas it scales up, and the water comes through warm rather than hot.
On a boiler with a cylinder
Check the timer
Is hot water switched on and inside its programmed time? A programmer that lost its settings after a power cut is a common culprit.
Check the cylinder thermostat
A dial on the side of the cylinder, usually set to about 60 degrees. If it has been knocked down, the boiler thinks the water is hot enough.
Feel the pipes
With hot water called for, the pipe from the boiler to the cylinder should get hot. If the boiler fires but the pipe stays cold, a motorised valve isn't opening.
Use the immersion
Most cylinders have an electric immersion heater as a backup. Switch it on and you will have hot water in an hour or so while you wait for the repair.
- Motorised valveDirects the boiler's heat to the cylinder, the radiators or both. The motor or the microswitch inside fails, and one of the two stops working.
- Cylinder thermostatFails so that it never calls for heat, or never stops. Cheap to replace.
- PumpIf the pump has failed, neither heating nor hot water works properly, and the boiler may overheat and lock out.
When to ring
If the checks above haven't brought the hot water back, ring rather than keep resetting. Say whether you have a combi or a cylinder, whether the heating works, what the display shows, and the make of the boiler. Most of these faults are a part Ian carries on the van and can fit on the visit. Anything specialist is ordered the same day and fitted as a priority.
If you can smell gas, this is not a heating problem. Turn the supply off at the meter if it's safe to, open the windows and ring the National Gas Emergency Service on 0800 111 999 before anyone else.
Diagnostic visit
- Cost
- Discussed when you ring
- Covers
- Finding the fault
- Parts
- Agreed before fitting
- Hours
- 7 days
Questions
The heating works but there is no hot water. What is wrong?
On a combi it is often the diverter valve or the hot water sensor. On a system with a cylinder, check the cylinder thermostat and the timer first. The no hot water guide goes through what to check before you ring.
There's a fault code on the display. What does it mean?
Codes differ by make. Note the code and ring. Some point to a blocked condensate pipe in cold weather, which is a quick fix; others point to the fan, pump or ignition. Repeated resets can make a fault worse, so try once and then ring.
Can you come today?
Ian works seven days a week and fits breakdowns in where he can. Ring rather than filling in the form, say what the boiler is doing and your postcode, and he'll tell you when he can get to you. If it's urgent, say so and he'll see what he can do. There's no extra charge for evenings or weekends.
Do you charge for coming out?
Ring and tell Ian what the boiler is doing. He'll talk it through with you and give you an idea of the cost before he comes out. Anything bigger than usual is priced once he has seen it.