DIY Doctor UK DIY Forums

Hope you lot can help me with this.....

I have a fairly old system, boiler from mid/late 90s, electronic timer from similar time. Always worked fine until a few months ago it started playing up - the hot water wouldnt come on when supposed to. the timer sys its on but the boiler and pump doing nothing.

switch on the heating and the water comes on too. you can also just have the heating on if you want, and that's fine.

so: HW on = nothing happening
HW on and CH on = working correctly
HW off and CH off = working correctly

Any thoughts before I just buy a new electronic timer / controller??

The timer could be the culprit, but so could other controls such as a cylinder stat or a motorised valve.

thanks for the reply.

Is there any way I can figure out what is at fault?

My thought is that it cant be the thermostat because when the HW is switched on at the timer, it actually comes on and off with the CH. So the stat must be OK?

Motorised valve? As in it is stuck in a position? Wouldnt that mean that the pump and boiler still come on when the HW is switched on, but it would heat the CH instead.

Appreciate your help.

greedypebbles wrote:
My thought is that it cant be the thermostat

If you mean the room stat, then no, this is probably the only thing you could cross off the list.

Really, it is a bit difficult to be precise, as there are numerous different timers and heating circuit designs and you don't mention which you have.

The Honeywell "S" Plan, "Y" Plan and "W" plans are the most common, and are all very different

You could test the timer by fitting a link wire across the HW contacts effectively bypassing the relay contacts, but whether you could achieve this really depends on your expertise. Obviously, there is a shock risk, and if you get the wires mixed up, you could end up worse off than you are now!

plumbbob wrote:

greedypebbles wrote:
My thought is that it cant be the thermostat

If you mean the room stat, then no, this is probably the only thing you could cross off the list.

Really, it is a bit difficult to be precise, as there are numerous different timers and heating circuit designs and you don't mention which you have.

The Honeywell "S" Plan, "Y" Plan and "W" plans are the most common, and are all very different

You could test the timer by fitting a link wire across the HW contacts effectively bypassing the relay contacts, but whether you could achieve this really depends on your expertise. Obviously, there is a shock risk, and if you get the wires mixed up, you could end up worse off than you are now!

I meant the thermostat on the hot water tank, but my thought still applies.

I dont know anything about the three plans you talk about so i cant comment on that.

the link wire idea is one i'll try and see what happens.