Central heating only runs when hot water is switched on

  dave010 14:39 08 Dec 2013

If there are any plumbers who could answer this I would be grateful.

I have a problem with my central heating system that has been like this for years. In order to run the central heating I have to have my hot water switched on. It is a 13 year old conventional boiler (potterton) and gets serviced every year. I have just had a new central heating pump and electric divertor valve replaced on a desperate fault but the problem still persists. I have mentioned this to the british gas engineers who conduct the service but none of them get stuck into the problem. Thanks in advance


  namtas 15:23 08 Dec 2013

It could be any number of things that give you this problem, but it is most likely that there is a cross connection in the wiring at the distribution block

click here

  Pine Man 16:46 08 Dec 2013

I don't profess to know the answer but I sure as hell know that British Gas need a good kick up the arse.

You have been paying them to maintain your system for years and they still have not fixed it!!!!!

  bumpkin 16:52 08 Dec 2013

First guess if doing it for years is that it is not wired correctly, does your controller give the option of CH only.

  Batch 18:36 08 Dec 2013

I think you will find this is quite normal. I've asked a couple of CH guys in the past and they've said it is quite normal (they had a "name" for it, but I can't recall).

I have a Drayton Tempus Seven 7 day Programmer (quite a number of years old now, not a new fangled thing, but still with an LCD display). It has two settings (adjusted by a plug in bridge on the back of the unit):

  • CH & HW switch together (i.e. the bridge is in place). SO if either CH or HW is switched on, the other is on as well.

  • CH & HW (supposedly) switch separately. It works that way if just HW switched on. But if CH switched on the HW always comes on (there must be an internal relay that forces this).

It may be that more modern programmers don't enforce this, but I think it is just the way that it used to be. It might go back to times when the HW used to be gravity fed (no pump to HW cylinder and possibly no cylinder thermostat), and so the very fact of the CH being on meant that HW would get heated regardless (you could not stop it) and the programmers followed suit.

  Batch 18:47 08 Dec 2013

BTW, just 'cos I'm saying it is "normal" doesn't mean I think it is good!

Suggest you ask your question on a site like diynot.com (in the CH / plumbing sections)

  Ventad 20:02 08 Dec 2013

You say that you have had a new "diverter valve" fitted this is different to a "mid-position" which will either close off the HW port and send the flow through to the CH or the if the cylinder stat is calling and not the CH thermostat the CH port would be closed and flow to HW cylinder, if of course both stats are calling the plunger or ball will rest in the midway position allowing the flow through both ports until either one or both stats are satisfied

If your system has been upgraded from gravity HW and pumped CH to a 3 port "diverter valve" or it was fitted from new with a "diverted valve" it is working correctly , you should not change the bridge as you call it in the system programmer the diverter valve is working correctly in that when you put both on on the programmer the HW will be satisfied first before the CH valve changes to CH. And in the summer/spring you flick off the CH on the programmer.

62 is about the right temp for the cylinder stat any higher if you are in a hard water area the cylinder will fill up with chalk.

  Fruit Bat /\0/\ 20:07 08 Dec 2013

My old (27yrs - changed last year) Potterton system was like that because it only had a two way valve and the plumbing to suit.

could set to HW only in summer but winter was HW and CH

No tank stat so water temp regulated by stat in boiler. CH temp was controlled by room stat that shut the valve to the rads when rooms warm enough.

  bumpkin 20:20 08 Dec 2013

sdave019trong text Does your controller give the option of CH only or not?

  bumpkin 20:27 08 Dec 2013

Not me intending to shout, something to do with the site formatting, anyway can you also confirm that the new valve you had fitted is 3port i.e. it has 3 pipes connected to it.

  dave010 20:33 08 Dec 2013

Thanks for all your help guys..I am pretty sure the 3 way diverter valve is working correctly as I can see it changing state and this leaves it with the wiring...With the wiring diagrams supplied on here I am going to check it for errors and possibly a cross short. The controller does has the option for CH only but it has been like this since the house was built 13 year ago and the system installed by the house builder.

I will let you know how it goes....thanks again :)

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