Separate heating & hot water...?

[Roger465]

Hi again folks – I have a Grasslin Towerchron QE2 controller on my central heating system (probably installed when the house was built in 1994.


The instructions say you can set programmes separately from heating and hot water, and indeed you can – but then the hot water always comes on with the heating, disregarding its own program. I want to program the hot water separately, as I have things like dishwasher and electric shower, so have virtually no need for hot water, and it seems a dreadful waste.


I can’t tell you too much about the rest of the system, except to say I’ve just had a new boiler fitted, and two new pumps (one for heating, one for hot water), but that hasn’t affected anything – it was like this with the old kit too.


I’ve reset the controller and very carefully programmed things separately, but to no avail. Is this a problem with the controller, or I understand there are things called “zones” in plumbing which may affect what can do what…?


Thanks

Roger

 

[stem]

The QE2 has two settings, one is where it is used with fully pumped systems that have motorised valves controlling the heating and hot water. In this instance it can be selected to provide independent control of both. The second setting is for older systems that don't have these valves and the plumbing means that it is not possible to have the heating on without the hot water being on at the same time. (Vice versa is OK)

It would appear that yours is the latter, and the programmer has been set by the installer to the second mode of operation due to the restrictions of the plumbing.

 

[Roger465]

It would appear that yours is the latter, and the programmer has been set by the installer to the second mode of operation due to the restrictions of the plumbing.

Thanks, that’s very kind of you. To help my understanding a little… as far as I know (which isn't very, as you’ll gather) my system is very simple – one boiler, two sets of pipework and two pumps.


My previous house was much newer, and had what I think must be the motorised valves you're talking about – again, one for heating, one for hot water – but only one pump. So I guess, in that kind of system, when the boiler’s on, the pump runs, but where the hot water goes depends on the states of the two valves?


So… am I being naive to believe that (in my current system) it’s simply a matter of two programmes switching the two separate pumps on and off? In which case a different controller might provide what I need…?

 

[denso13]

Unlikely. You'll need the pipework altered and zone valves fitted. How much of a job that is depends on the existing layout.

 

[stem]

Two pumps. That is a bit unusual, although not unknown. Whilst if one pump is for the hot water and the other for the heating then switching them on and off separately is quite achievable. However, the problem is the boiler, because both hot water and heating need the boiler to operate, and usually the hot water controls the boiler. So to have the heating on, the hot water also has to be on to operate the boiler.

You could always switch the QE2 into fully pumped mode, turn on the heating only and see if it comes on. If it doesn't you will know if your system is unsuitable without being modified.

Edit
How to change QE2 to 'fully pumped' added below.

The QE2 is capable of the independent control of heating and hot water that you want. Any restriction will be with the existing installation, so changing the programmer won't help.

 

[Roger465]

Two pumps. That is a bit unusual, although not unknown. Whilst if one pump is for the hot water and the other for the heating then switching them on and off separately is quite achievable. However, the problem is the boiler, because both hot water and heating need the boiler to operate, and usually the hot water controls the boiler. So to have the heating on, the hot water also has to be on to operate the boiler.

Yep that’s definitely what I have…

I kind of assumed (hoped!) that the boiler could sense any kind of cold water passing though it, ie via the heating pump OR the hot water pump. But that was Mr Spock-type logic, rather than any kind of knowledge…


Think we’re hitting the limits of my understanding very quickly here, so I’ll ask the plumber to adjudicate when he comes round again in a week or so for a different job

 

[Hot&Cold]

edit, following photo above,

 

[Terrywookfit]

Yep that’s definitely what I have…

View attachment 128709

I kind of assumed (hoped!) that the boiler could sense any kind of cold water passing though it, ie via the heating pump OR the hot water pump. But that was Mr Spock-type logic, rather than any kind of knowledge…


Think we’re hitting the limits of my understanding very quickly here, so I’ll ask the plumber to adjudicate when he comes round again in a week or so for a different job

I told you in your previous thread..........

"It has nothing to do with the boiler. It knows not what the demand is for.

I notice you have two pumps. are there any motorised valves... or a relay to control them??"
You seemed more concerned about fuel consumption and pictures of dodgy shelving!!

Without motorised valves or a relay to separate the pump supplies. They will both run at the same time.

 

[Roger465]

I notice you have two pumps. are there any motorised valves... or a relay to control them??" You seemed more concerned about fuel consumption and pictures of dodgy shelving!!

No, I wasn’t more concerned with shelving – the conversation in that previous thread had entered areas I didn’t understand, and discussions between people who did. I was just trying to provide some light relief. Oil consumption remained/remains my main concern, yes. That’s why I spent a small fortune on a new boiler. Or should I say burner/boiler?


As regards your questions about motorised valves and relays – with respect, how would I know? I’m just an ordinary DIY enthusiast, trying to figure out and separate the things that I can do from those I can’t.


I THINK I know what a motorised valve is; I THINK I can recognise one, but I’m not certain. The picture here shows what I BELIEVE to be the totality of my system, apart obviously from the hot water tank (which doesn't appear to have any kind of gubbins with it) and the controller.


The two pumps appear to connect directly to the mains via two switches on the garage wall; they don’t appear to be “controlled” in any way. You can switch them on and off via the wall switches. My belief (possibly completely wrong) has always been that the boiler just sits there waiting till cold water passes through it, upon which it switches on and starts boiling… when the water reaches a predetermined temperature, it stops again.


I had hoped – and it looks like I’m wrong – that it had kind of two separate water “circuits” through it (ie 2 pipes), one for heating, one for water; each pumped by one of the pumps on the wall, and that the presence of cold water circulating in either would turn the boiler on. I figured it would then heat whatever was passing through it.


Guess I was wrong…

 

[Terrywookfit]

Try turning the hot water pump off with the wall switch..... (The ones not in view on photo) !!

 

[Roger465]

Try turning the hot water pump off with the wall switch..... (The ones not in view on photo) !!

Sorry about that – hopefully this shows it better. Ummm… seriously, could I just do that? It had occurred to me, but I’m not sure whether you’re joking or not!

It's those two light switches at the top...

 

[Terrywookfit]

No I'm serious.
Just make sure one of them is working to prevent overheat stat on boiler tripping.

 

[Roger465]

No I'm serious.
Just make sure one of them is working to prevent overheat stat on boiler tripping.

Thanks. So, in general terms, what actually brings the boiler to life - is it both powered on by the control unit, and the temperature of the water flowing through it?

 

[Terrywookfit]

At a GUESS I would say Water on at programmer activates boiler and hw pump. Htg on via roomstat if fitted turns htg pump on.
That's why you need hw on at programmer to get htg.

Boiler fires if boiler stat is calling.

 

[Roger465]

No room stat, sadly just the little one on the boiler, which doesn't seem to do much tbh...