hot water when c.heating on BUT none with just hot water on All aspects of plumbing questions and answers, help, tips and information

[lb]

hi,
any help out there as i cant get hot water unless the c heat is on - the boiler doesnt seem to stay lighted with just hot water switch on - pipes only get warm whereas boiling hot when c.heat on. any ideas apprec-but please in simple speak if poss.hot water tank is in loft-is an old gravity pipe system i think. thought might be air lock but obv get hot when cheating on. thanks lb

[jondeau]

Sounds like an electrical problem with whatever control system you have.

[Arnak]

Hi,

Yeah sounds like a control valve problem if one is fitted.

On some systems you can have hot water only or ch + hot water.

Check to see if there is an electrical 2 way valve fitted.

If there is then there should be a lever on the side to operate it manually so you can check it that way.

Arnak

[Paul Pepper]

Most likely an air lock. Can be very difficult removing in some systems. What type of boiler is it?

[lb]

many thanks all for the replies - where do I find the control valve - near the boiler downstairs or in the loft near the hot wat tank?
Secondly - we do have a prob with air in pipes a lot - has been cured in past but i thought if got hot water when c heat on - this would not be the cause? have tried to flush any air out also - though maybe didnt succeed
cheers lb

[lb]

sorry - yes its a Halstead mark 2 boiler

[Arnak]

Hi,

The valve would most likely be near the boiler, there should be a cable from the control unit leading to it.

Unless as I said it has been placed somewhere more unusual.

Arnak

[jondeau]

Right....

...It's very difficult to diagnose faults without seeing the system, so the easiest way to be certain of the problem is to take it step by step.

It's an old system with a gravity fed hot water cylinder, lets assume that when it was first installed it did work.

With the type of system, all that is needed for the hot water to work is that the boiler fires up. The pump is only there to push water through the radiators.

When the boiler is cold, switch on the hot water function only. Does the boiler ignite and burn ?
If it does not, then the problem is is an electrical one and you need to check the wiring between the hot water switch and the boiler.


If it does, and stays lit until the boiler switches off with it's built in thermostat then there is some restriction in the flow and return pipes from the cylinder.........

......and then you really do have a problem.


In this case.....assuming it did work originally, the pipework to and from the cylinder should be correctly installed........so, scale?.......sludge ?

With this sort of system, it was usual for the cold feed pipe, and the vent pipe from the heating expansion tank to be fitted to the gravity flow and return pipes where they enter the cylinder, and this would normally keep the flow and return from airlocking.......



JD

[lb]

Ok many thanks to you both - I will check re lever but am not sure if there is one - secondly - the boiler does fire up when on hot water only - but switches off after a few mins - it does re fire up every so often and pipes get warm (one flow and return pair) whereas there is another pair of flow and return pipes that do get very hot. However - it still does not heat the water.

I know this has happened before and seemed to be air - but i just thought this time would not be the case as when i select the c.heat/hot water option it DOES get both pairs of pipes very hot and thus hot water.
cheers! Lb