Honeywell ST9100C set to 'off' but boiler still provides domestic hot water.

[Pidgeonpost]

Hello folks - first post here.

Last week our faulty Honeywell ST6100C programmer was replaced by a ST9100C, this being the Honeywell-recommended replacement. Our regular heating engineer did the swap because the backplate was stuffed, so a simple DIY clip-on swap wasn't possible (by me at least 😄).

This programmer controls our Grant oil boiler, but a feature we dislike on both the old and new programmers is that the boiler provides domestic h/w even when the programmer control is set to 'off'. This is darned annoying as the boiler kicks in at night, which is noisy and it's only heating and reheating hot water that we don't use! We use very little hot water during the day and this continuous cutting in/out just uses more oil - though how much I don't know.
We can overcome this by turning the whole system off at the switched spur that provides power, but it seems the wrong approach. Surely 'off' should mean 'off''?
I've read the Honeywell booklet and it doesn't help on this score, so I'm wondering if anyone can shed some light please?
Thanks.

 

[SJB060685]

Are you on an S plan system? Two 2 ports in the airing cupboard usually, one for CH and one for HW.

 

[Pidgeonpost]

Thanks for your reply. I should have said, but we have no hot-water cylinder - it's a 'hot water on demand' system.

 

[SJB060685]

So you have a Grant combi boiler? What's the model of boiler please and I will find a wiring schematic. Sounds like you have the boiler set to heat the slave tank constantly and not timed, which is what you would prefer.

 

[Pidgeonpost]

Combi! That's the word I couldn't remember!
It's a Grant 70/90, outdoor job. It's pretty old - 2003 I think. It's been serviced regularly, but has cost us a bit the last couple of years.

 

[SJB060685]

I'm just on the phone to Grant trying to source the right manual. In the mean time is there a rocker switch on the boiler panel for hot water and if so is it set to constant?

 

[SJB060685]

I've just got off the phone from Grant technical. He's sent me two manuals but neither appear to be the right one for your boiler. Can you see if the boiler data plate can clear up exactly which model it is.
He did mention on some of their older models you couldnt have CH without HW being on as well. Another possibility is there's an internal link by passing the programmer, or something I should mention is perhaps you have a two channel programmer but it only controls the CH a HW is wired in as constant at the boiler. If you take the head off your programmer and expose the base plate how many wires are in there?

 

[SJB060685]

Update. I have been informed by an associate that this boiler is not actually a Grant. It's a cheap Grant badged as a Eurocal. The programmer you have is actually a single channel programmer which only controls the central heating, therefore your hot water is wired in to be permanently on within the boiler. I'd imagine you could rewire it so you could time your hot water but without seeing the correct manual I couldn't say for sure as as I pointed out above some older combis that wasn't possible.

 

[Pidgeonpost]

Well, thanks for taking the time and trouble trying to sort this out. I've had a closer look at the data plate, which was partially hidden, and although it says it's a 70/90, it's not a Grant 70/90 as your colleague suggested. The programmer is indeed a single channel one.
We inherited this boiler when we moved here over 10 years ago and accepted that it was a Grant as it had the same look and model number as at our last house which had a genuine Grant boiler.
We've lived with this irritating 'feature' for 10+ years, so I guess we'll revert to our old habit of just switching everything off at the switched spur overnight again. 😔
Chances are we're going to be looking to replace in the next few years. That'll be a whole new can of worms no doubt! 😄
Thanks again for all your help.

 

[SJB060685]

Well, thanks for taking the time and trouble trying to sort this out. I've had a closer look at the data plate, which was partially hidden, and although it says it's a 70/90, it's not a Grant 70/90 as your colleague suggested. The programmer is indeed a single channel one.
We inherited this boiler when we moved here over 10 years ago and accepted that it was a Grant as it had the same look and model number as at our last house which had a genuine Grant boiler.
We've lived with this irritating 'feature' for 10+ years, so I guess we'll revert to our old habit of just switching everything off at the switched spur overnight again. 😔
Chances are we're going to be looking to replace in the next few years. That'll be a whole new can of worms no doubt! 😄
Thanks again for all your help.

You might find it's possible to wire it in so you can have timed control. Of course you would need a two channel programmer, some cable and someone capable of wiring it correctly. If you could source the correct manual you would be able to tell for sure.
Of course you can carry on as you are and keep switching it off overnight, however this would me the heat store will run cold and you would need to let that come back up to temperature in the morning before having hot water, continuing this method will also slightly increase your fuel bill.

 

[Pidgeonpost]

You might find it's possible to wire it in so you can have timed control. Of course you would need a two channel programmer, some cable and someone capable of wiring it correctly. If you could source the correct manual you would be able to tell for sure.
Of course you can carry on as you are and keep switching it off overnight, however this would me the heat store will run cold and you would need to let that come back up to temperature in the morning before having hot water, continuing this method will also slightly increase your fuel bill.

I might have a look at the manufacturers website when I get chance to see if there's a manual I can download. It probably won't make much sense to me, but we've got a very good electrician lined up to do some work for us, so I might get him to have a look. Our regular heating engineer is a good bloke but he's got major health problems and I don't want to bother him on something that's not an emergency.
All the best, and thanks again.

 

[ShaunCorbs]

Or email the manufacturer

Turco Engineering | Northern Ireland

Experts in Sub Contract Engineering | Boiler parts and spares

www.turco.co.uk

 

[Pidgeonpost]

Or email the manufacturer

Turco Engineering | Northern Ireland

Experts in Sub Contract Engineering | Boiler parts and spares

www.turco.co.uk

Thanks Shaun.