CH Controls

[Beena72]

I've got a gas boiler, which was previously controlled by a potterton ep2002 programmer. I have now installed a Drayton RF3 thermostat in series with the central heating switch of the Potterton, and obviously run the Potterton switched to constant, letting the Thermostat take control. I'm happy with that, and it's all commissioned and working, but what I wanted to know was why the Potterton controller automatically switches the Hot Water on whenever the Central heating is on.

Is this something to do with the way the boiler operates, in that it may damage the system if it ran CH without HW, or is it just some ill thought out convenience feature?

I'd like to bypass the Potterton for the central heating, so i can then run the hot water under timed programming, but obviously don't want to if this may cause a problem during the times when the central heating is called but the hot water is off. Any help in clearing this up would be greatly appreciated.

 

[*rab*]

I'm not a plumber, but it sounds like you have a gravity-fed system - you have the HW on the programmer connected to your boiler, and the CH connected purely to the CH pump. If this is not the case then it sounds like you have your programmer set to the "G" position in error.

If a programmer is set to "G" then the HW will turn on automatically when the CH comes on, otherwise the boiler won't fire up.

 

[*rab*]

I'm not a plumber, but it sounds like you have a gravity-fed system - you have the HW on the programmer connected to your boiler, and the CH connected purely to the CH pump. If this is not the case then it sounds like you have your programmer set to the "G" position in error.

If a programmer is set to "G" then the HW will turn on automatically when the CH comes on, otherwise the boiler won't fire up.

 

[chrishutt]

As Rab says, if you have gravity circulation to the hot water cylinder, then the HW is bound to be on when CH is on, so programmers for this set up do not allow you to select CH without HW.

If you now have separate control of HW (e.g. via motorised valve) you can control the HW independently, setting programmers to allow this.

 

[Beena72]

Thanks chaps (if, indeed, you are chaps),

So basically my system works by heating water at the boiler, which then rises naturally up to the cylinder, and circulates like that. All that happens when i switch the CH on, is that the pump kicks in and sends that same water all around the house.

That would then explain why the upstairs radiators warm up when the hot water is on.

By putting my thermostat in series with the central heating switch then, i'd need the hot water to be on whenever the central heating kicked in, or it would just be pumping cold water around the house. So i might as well just leave the hot water on constant, the other option being that i run them both when the thermostat calls at the risk of having no hot water if it's a warm day.

I want a combi again, i understood that...

 

[Agile]

I dont think that I understand what you are saying but I may be able to explain it more clearly for you.

In the simple case you would have a timeclock to switch on the boiler at your chosen times. That would heat your water!

In addition you would supply the pump from the timeclock output via the room stat to bring on the heating when you need it.

If you had a two channel programmer then you could run the hot water when you want it and IF the programmer allowed it you could then run the heating for different times within the HW times.

You have to understand that your system is quite old fashioned and not very efficient. Most programmers are designed on the assumption of a fully pumped system and will not necessarily allow them to be wired as required for what is described in the previous paragraph.

Tony Glazier

 

[Beena72]

Thanks Agile,

To put it simply I can't have Central Heating unless the Hot Water is on with the system i've got. I therefore need to keep the Hot Water 'On' constantly in order to be able to control the Heating via thermostat rather than timer. And there's no way around that without fundamental changes to the system.

Is that right? So much for getting a thermostat to reduce fuel use, sounds like it'll be worse now.

 

[ricarbo]

Your new programmer will allow separate control, but only if you add some plumbing bits. If you add a thermostat tied on to the outside of the hot water cylinder and a 2 port motorised valve, you can get the heating side to be on when the water is off. The wiring scheme to do this might require an extra relay, but the cost of the bits needed is probably under £50. Obviously if you have someone do it for you, you'll have to pay for their time. You could do a bit more on the pipework side and alter the system so the pump does both heating and hot water, via a 3 port valve instead of the 2 port valve, which would get the water heated more quickly. You could add an anti-gravity flow valve to stop the rads heating when just the hot water is on eg summer (or you could turn the boiler off and heat the water with your immersion heater on a timer, perhaps getting the electricity changed to cheap rate for overnight - often no charge for this change)

 

[Agile]

I doubt that Beena72 has the plumbing and electrical skills to do all that!

Come to think of it there are many CORGI registered people who could not do it either!

Tony

 

[Beena72]

The assumption is (sadly) quite right Agile, new kitchen or bathroom plumbing is ok, but this central heating mularkey is just a step or two too far for me.

I think i'll leave it as is unless the next gas bill is horrific.

Thanks for all your help.