Hive heating only works when the hot water is turned on at the same time

[happycat_ishappy]

Hi Guys, I recently replaced my nasty old thermostat for a Hive system and it all seemed to go well, the app sees both heating and hot water and they turn on as expected and fire up their respective pumps.

However, the heating doesn’t seem to fire the boiler so we’re only getting heating if the hot water is on at the same time.

Is that something I’ve wired wrong or should my hot water be back to the way it was and basically always on (so connected back into that grey box)?

 

[stem]

Probably because the way that the system is wired means that only the hot water channel turns the boiler 'on'. If this is the case, then some re-wiring to add a couple of relays to the two pumps and then to wire each relay so that it switched the boiler 'on'. This would mean that if either HC or HW were required the boiler would run. [Systems with motorised valves have a small switch internally that carries out the same function]

If as I suspect, only the HW channel is controlling the boiler, then with the previous controller it would have been the same. It wouldn't have been possible to have the CH on without the HW being on as well.

Hive can handle such systems, and you would need to select 'Gravity' mode of operation. Then whenever you selected CH, the HW (and the boiler) would come on as well. Although yours is fully pumped it doesn't fit the description below, but the wiring functionality is configured as per a gravity system.

 

[happycat_ishappy]

Thanks for the reply! Thing is the first day I just replaced the timer as I wasn't going to bother with the hot water. And on that day it worked, from the app I could fire up the heating great.

The next day I decided to tidy the cabling as I was happy it worked and at the same time cabled the grey box into Hive too as I figured that controlled the hot water.

hot water worked great too so I assumed it was all working until yesterday when I noticed that the boiler wasn't kicking in when the heating came on unless the hot water was on.

So I can't work out if it's something that stopped working since or if the grey box that I disconnected somehow controlled the heating switch to the boiler too?

 

[happycat_ishappy]

Should add, prior to me installing Hive, only the heating had controls. Hot water seemed to almost always be on with a temp control dial next to the tank, but also one on the boiler (that BG just told us to set to max and control water temp from the one by the tank).
So our hot water has never been on a timer or anything, just always heating the tank really.

 

[stem]

I don't know your electrical skills, but it would involve following the switched live wire from the boiler back to the Hive and seeing where it's connected. If it is wired as I suspect it will terminate at the Hive HW on.

No idea what the grey box is. I can only see part of its cover. It could be a hot water cylinder thermostat in which case if you have disconnected it then you have lost thermostatic control of the hot water and it should be re-installed, can't see it would solve the other problem though. Might just be a junction box. I can't tell.

I suspect with this one though it maybe beyond the scope of something that can be done over a forum and will need a pro to come and physically inspect the whole installation to resolve.

 

[ericmark]

The normal way is to use a single pump and motorised valves which have micro switches in them so work like a relay. I have twin pumps, and only way to activate the boiler with either pump is to use a relay, well two one for each pump.

I have a relay, so I can heat main house without heating the flat, it seems who ever fitted the central heating in my house was unaware they are centrifuge pumps not positive displacement, so even if one pump does not run, you will still get water circulating, in my case in the reverse direction.

Either it needs a non return valve, or motorised valves to stop water flowing.

However Hive has the option for thermo-syphon DHW, and what it does is activate one set of contacts for the pump, and other for central heating boiler, so if the DHW pump and boiler goes to one set, and the CH pump just to the other set, it would work, but can't have CH without DHW.

Now since you have a DHW thermostat, if that is put in the pump supply, it would give some control of domestic hot water in winter, however what you want is in summer to be able to have DHW without CH and leave the boiler switched on, but it will only fire up when required, I can't of hand see a way to do that with controls you have.

Since you have RCD's on each pump it would be easy enough to switch pumps off to test what happens.