Help please! Adding wireless room thermostat to dual pump system

[dram773]

Hi all, new owner here looking for advice ...
There is a Grant Euroflame 70/90 oil-fired boiler with two pumps but no motorised valves. I assume one pump is CH and the other for DHW, so the valves are not needed. There is a cylinder stat and a Sangamo Choice PR2 two-channel programmer wired to HW-on (t3) and CH-on (t4) but no room thermostat. We would like to upgrade the programmer to include a wireless room thermostat. The previous owner installed a Hive as a simple swap for the Sangamo, but swapped back for the sale and apparently no wiring changes were needed (they both use the standard backplate).
We don't need the 'smart' facilities of the Hive, so I was hoping to install a Honeywell Sundial RF2 Pack 2 as a similarly simple swap for the Sangamo. But as our dual pump system is not a standard S-plan, is this likely to cause any problems?
Many thanks

 

[SJB060685]

I advise you to replace the two pumps with a single one and have an S plan configuration installed. The moment you have more than one pump the wiring can become complicated and you need a suitable relay and someone who knows how to wire the systems.
That's not to say what you want can't be achieved with two pumps but that's my advice.

 

[dram773]

Sound advice, I'm sure, but the system works fine with both the Sangamo programmer and the Hive with no wiring changes. Does that suggest a relay has been installed somewhere?

 

[SJB060685]

I'd imagine so yes mate but without being there I couldn't say for sure. Does the CH come on when there's a demand for HW and vise versa? If so then probably no relay installed. If you have independent control then there probably will be a relay.

 

[dram773]

I'd imagine so yes mate but without being there I couldn't say for sure. Does the CH come on when there's a demand for HW and vise versa? If so then probably no relay installed. If you have independent control then there probably will be a relay.

Thanks for your help. To be honest. I haven't tried that test - was just happy to have CH and DHW when I switched it on and haven't had system on since, despite the disappointing summer (haven't needed CH, using immersion for DHW). Will try your suggestion this w/end.
If it is all working as you describe, do you think I can just swap in the Honeywell to get a room stat? The vendor says it all worked fine when he swapped in the Hive.

 

[SJB060685]

Thanks for your help. To be honest. I haven't tried that test - was just happy to have CH and DHW when I switched it on and haven't had system on since, despite the disappointing summer (haven't needed CH, using immersion for DHW). Will try your suggestion this w/end.
If it is all working as you describe, do you think I can just swap in the Honeywell to get a room stat? The vendor says it all worked fine when he swapped in the Hive.

If the system is suitably wired then yes, however if you don't have independent control then one will always bring on the other.

 

[dram773]

If the system is suitably wired then yes, however if you don't have independent control then one will always bring on the other.

So are you saying that the worst case scenario is that CH and DHW will both be on when either one is calling for heat? I could live with that for the time being. What I don't want is to swap the units over and end up causing damage to a system which, while inefficient, is at least working - especially when it seems that local professionals are fully booked until next year .....

 

[SJB060685]

That's what I'm saying yes. As I said in my original response as soon as you have two or more pumps controlling different zones on a system then a relay/relays are needed. Otherwise when power is sent to one pump and boiler the other pump is energised as well.
The system you're describing is quite common on oil, certainly older systems and you may find the system has controls to compensate, unfortunately though in my experience this is most often not the case
If you discover at the weekend the system is performing as above then a relay can be purchased quite cheaply and with a bit of wiring alterations can be sorted quite soon.

 

[dram773]

That's what I'm saying yes. As I said in my original response as soon as you have two or more pumps controlling different zones on a system then a relay/relays are needed. Otherwise when power is sent to one pump and boiler the other pump is energised as well.
The system you're describing is quite common on oil, certainly older systems and you may find the system has controls to compensate, unfortunately though in my experience this is most often not the case
If you discover at the weekend the system is performing as above then a relay can be purchased quite cheaply and with a bit of wiring alterations can be sorted quite soon.

 

[dram773]

Thanks, again. I wouldn't feel confident choosing a relay and changing the wiring, so I'd get someone in to do it - swapping one programmer for another on the same backplate is about my limit

 

[Tilerdon]

I have a two pump system and had similar problems when we bought our bungalow 2 years ago. It was a right mess in terms of operation. I have a 4 pole contactor which was originally incorrectly wired but I have now installed a zone valve on each circuit. We have a conventional 2 channel programmer and a programmable but wired hall thermostat. I have just de-installed a Sundial because I have just changed all my standard TRV's for smart ones.
I can provide you with a wiring diagram for the system if you would like it.

As I said in a previous post about the TRV's, as soon as I mentioned 2 pumps to any heating engineer they declined to even take a look

 

[dram773]

I have a two pump system and had similar problems when we bought our bungalow 2 years ago. It was a right mess in terms of operation. I have a 4 pole contactor which was originally incorrectly wired but I have now installed a zone valve on each circuit. We have a conventional 2 channel programmer and a programmable but wired hall thermostat. I have just de-installed a Sundial because I have just changed all my standard TRV's for smart ones.
I can provide you with a wiring diagram for the system if you would like it.

As I said in a previous post about the TRV's, as soon as I mentioned 2 pumps to any heating engineer they declined to even take a look

Many thanks for your kind offer. We've decided to live with the lack of independent CH/DHW for the time being, as at least we should be warm over the coming winter months!