Replacing A Dhw And Ch Programmer

Existing aged programmer (Potterton) only allows Central Heating to be on when the Domestic Hot Water is on.

I think this is a leftover from the old central heating system which has been partly modernised. What needs to be done so that the CH and DHW can be switched separately?

Is it just a case of move a hidden setup switch in the programmer or will plumbing changes need to occur?

Ideally a modern programmer will be fitted and I'd like to best advise my customers. They'd like a new one so that it doesn't lose settings everytime power goes off, looks nicer, and runs the system more efficiently.

FYI, System:

Old: Boiler was in cupboard under stairs along with pump and valves, wired room stat in hall (in Farenheit!), wired 2 channel programmer in kitchen.

Currently: New boiler (MAIN HE system boiler) fitted in garage with pipework to understairs cupboard.

Wiring centre, pump, 3 port valve all in cupboard under stairs too. Hall room stat and programmer as before.

The 3 port valve looks like it was replaced when the boiler was, so in my mind the hot water and heating should be separately switchable but am grateful for all and any advice!

Thanking yous.

Dave.

It all depends on what controls you have and how it is plumbed.

Usually gravity fed hot water, which does not normally have any control valves, has to be on whenever the CH is on.

If the system has been re plumbed to fully pumped, with either a 3 port valve or two 2 port valves, then with a bit of rewiring you can have hw or central heating only, or both together.

It may just not have been set correctly, on the back will be a small switch for pumped /Gravity.

It should be set to Pumped but only if you have the correct wiring there to start with and not just Heating On and Hot Water On outputs, you also need output on Hot Water Off.

Also check the 3 port valve is actually a mid position valve and not a diverted valve,

Recently had a full blown row with a plumber over this, he didnt know there was a difference!

Thats the only reason I was called, different number of wires and he didnt know how to get it to work.

:shakehead

Why not ask the plumber what he has plumbed it in for? Then you can decide whether you have have enough cables in where you need them?

Thanks for all the great replies . I'll research some more this afternoon and report back.

ProDave said:

It all depends on what controls you have and how it is plumbed.

Usually gravity fed hot water, which does not normally have any control valves, has to be on whenever the CH is on.

If the system has been re plumbed to fully pumped, with either a 3 port valve or two 2 port valves, then with a bit of rewiring you can have hw or central heating only, or both together.

Click to expand...

I'd forgotten about the gravity thing, will check when there this afternoon.

Steve3948 said:

It may just not have been set correctly, on the back will be a small switch for pumped /Gravity.
It should be set to Pumped but only if you have the correct wiring there to start with and not just Heating On and Hot Water On outputs, you also need output on Hot Water Off.

Click to expand...

I'll report back with wiring configuration. Thanks.

steptoe said:

Also check the 3 port valve is actually a mid position valve and not a diverted valve,
Recently had a full blown row with a plumber over this, he didnt know there was a difference!
Thats the only reason I was called, different number of wires and he didnt know how to get it to work.
:shakehead

Click to expand...

ooh, that's a new one on me. How'd you tell the difference? Just by wiring or will they appear different? I'll take a piccie in a bit. Thanks!

Sharpend said:

Why not ask the plumber what he has plumbed it in for? Then you can decide whether you have have enough cables in where you need them?

Click to expand...

Wish I could but it was plumbed in a few years ago for the previous owners.