Hot Water alone doesn’t fire up the boiler

[Bradley31]

Hi, We have a problem with our Hot Water coming on. Sometimes it works and we have Hot Water and other times it doesn’t. There doesn’t seem to be a pattern that I can see. when it doesn’t work the only way to get the boiler to fire up is to put the heating on for an extra hour. When you cancel the heating the boiler turns off and we don’t get hot water still even though the thermostat on the tank knows the water isn’t up to temperature. Maybe it is faulty?
Any ideas would be greatly appreciate, I have tried all sorts and got it to work but then try the same thing later in the week and it doesn’t work. So I am a bit confused what to try next.
thanks

 

[Deleted member 120897]

It sounds like you have a 3 port valve, I would investigate this first.

 

[Bradley31]

It sounds like you have a 3 port valve, I would investigate this first.

There are 2 valves. 1 is hot water and the other heating. The HW valve opens and the light goes on for Hot Water etc but the boiler doesn’t come on

 

[Basher]

There are 2 valves. 1 is hot water and the other heating. The HW valve opens and the light goes on for Hot Water etc but the boiler doesn’t come on

What is the light that goes on please?
You may know that the switched live feed to turn on the boiler for hot water comes from a microswitch within the HW valve. The idea is that as the valve approaches the fully open position, a cam pushes the microswitch lever, which supplies power to the boiler. If the valve doesn't always fully open, maybe the switch is not being activated.
With care, it may be possible to see what is happening.
If you are competent with electrics, and have the relevant test instrument(s), you could check the above theory. Or get an engineer in!

 

[Bradley31]

What is the light that goes on please?
You may know that the switched live feed to turn on the boiler for hot water comes from a microswitch within the HW valve. The idea is that as the valve approaches the fully open position, a cam pushes the microswitch lever, which supplies power to the boiler. If the valve doesn't always fully open, maybe the switch is not being activated.
With care, it may be possible to see what is happening.
If you are competent with electrics, and have the relevant test instrument(s), you could check the above theory. Or get an engineer in!

Just the light on the control panel. I haven’t done a test of the connections or thought about the valve not always opening. Thanks for this. I will have a go tomorrow and see what happens.