Hot Water Only - Heating comes on?

[Steviebhoye]

Hi all,

Had a problem for a wee while now where turning the hot water only on also turns the central heating on? Room stat comes on etc. Strangely this only seems to happen when the hot water tank is not satisfied. ie. if I turn the tank thermo up a bit. Fed up with my local plumber as he fiited a new mid-postion switch and told all was OK but it is exactly the same as before. I am frustrated as this seems like a simple issue to me. The plumber told me that there was some fluctuation on his multimeter in one of the positions but as I understand it (read online) this how they are supposed to work.

Any advice, pointers would be greatly appreciated.

Thanks Steve

 

[Gasman28]

Does this happen when the room stat is set to zero and the programmer is on hot water only? What make of programmer / timer?
Did your plumber exchange the complete valve or just the powerhead?

 

[Steviebhoye]

Hi thanx for the reply!

Yes this still happens when room stat is set to zero and set to HW only

Honeywell ST6400C Timer

Honeywell Stat.

Plumber replaced just the electrical part is this the powerhead? (square metal box) he did not change the valve itself.

The problem is intermittent. Seems to working at the moment as expected.

Seems to somehow be related to the stat on the water tank, when turning stat clockwise on tank. Seems to happen shortly after both heating have been turned on via timer in the morning. Timer turns both off as expected then if I try to turn just water manually shortly afterwards this is when the problem occurs. Could this be sludge in the pipes? He said all the wiring was fine?

 

[Gasman28]

It could be that the valve is letting by ( partially stuck in the heating position ) due to contamination of the system ( scale, crud etc )
If you are compentent, you could try this when the system is cool:
Switch off central heating system electrically
Remove powerhead cover
Unscrew the powerhead from the valve body - two screws
With a small spanner, move the valve spindle back and forth - caution, minimum pressure required as the spindle only moves about 15 degrees each way.
Replace the powerhead on the spindle and then outer cover.
Switch on electrically and put programmer to 'hot water only'
Test to see if the pipe from the valve to central heating gets hot. Expect some warmth close to the valve.
Remember to use caution with electrics.
Good luck

 

[Steviebhoye]

ok thanx for that. I will wait for the plumber to come back and see what he says. Not really confident enough to mess about with it myself.

One question when heating is on, should the water in the tank also heat up as this is what is happening at the moment I think. My old system (back boiler) broke down about 10 years ago and this was due to crud in pipes - cost me over 1K to get it sorted - don't want that again! This condensing system has only been installed for 2 years.

 

[OilLecky]

Stevie,

I'm afraid that the thread is a bit hard to follow but if the hot water is selected "off" there should not be a supply to the cylinder thermostat. Are you saying that, with the central heating off, when you manually switch on the hot water, then increase the temperature setting on the Cylinder Thermostat, the heating comes on?
Can you get to the 3 way valve? Tell us what make and model it is or even better, remove the electrical power head and watch the thing move when you operate the controls.

 

[Agile]

There are some older systems and also some wrongly wired or set systems which ALWAY have the hot water on with the central heating!

We dont know about yours and it seems as if you "plumber" is not much use although intermittent faults are difficult for anyone to find.

A few weeks ago I went to a leaking two port valve with a trainee and opened the valve to show him why it was leaking. The ball's bearing was stiff so the ball was not rotating so the rubber of the ball had become depressed and that caused it to leak!

I managed to clean the bearing and lubricated it with silicone and I expect if I installed it at home it would have worked OK.

Tony

 

[Steviebhoye]

"Are you saying that, with the central heating off, when you manually switch on the hot water, then increase the temperature setting on the Cylinder Thermostat, the heating comes on?"

That is exactly what was happening. I have had my local 'plumber' round and he looked at the electrics with a multimeter etc. and told me that it was a case of 'trial and error' - didn't exactly fill me with confidence!

He has wired in a new head onto the mid-position pump and it seems better - but I am not convinced that all is as it should be. The heating light comes on for a second or two when turning just the water on! Also I am sure that when just the heating is on the hot water tank is heating up also? is this normal?

I am obviously not an expert at this I am just anxious to avoid getting charged a few hundred quid for something that isn't right.

Thanx a million for the advice - this really is a great forum.

Best,S.
[/i]

 

[OilLecky]

Stevie, I hope Agile and Gasman can confirm this, or perhaps clarify.
Much depends on how your system is laid out but I would have thought that if you have a mid-position, 3 way valve then you either get "hot water only", "hot water and heating" or "heating only". It is possible to get a few seconds of heating when hot water is selected because the actuator stays in the last selected position for a while when hot water is selected. However I would have thought that your hot water primary system was fed from one side of the valve and your heating from the other. I would not think that the the two would operate together unless the valve was always motoring to the mid-position. That would be a wiring problem I guess. I have seen many heating / hot water systems wired up incorrectly. Have you got a friendly electrician who can use a multi-meter? If so check out the Honeywell web-site where you can find suggested wiring circuits.
I still suggest that you take a look at the valve. Some models have a lever on the side that shows you what position it is in. Get someone to operate the controls while you watch it. (Often they are close to the hot water cylinder, so you can watch and listen to the valve when you operate the cylinder thermostat.)