Can a Hive installer take mercy on me pls?

[Terry Williams]

I am struggling to wire up a very simple gravity HW with pumped CH system. I have an old but much loved Grant triple-pass 90/110 oil boiler and a Grunfos circulation pump. I am in a gas free area. The defunct room thermostat is removed.
The Hive receiver is a dual channel type. It all works fine wired with the boiler and pump connected to “Heating on (NO)”. So, all is almost well.
Here is the difficult bit: I would like to be able to have hot water without the heating. NB I am happy with HW coming on when the heating is on. But, I’d just like to be able to turn HW on independent of the heating.
I wonder if anyone knows how to connect the pump and boiler to the Hive to achieve this?
I have tried several combinations but failed miserably as however I make the connections the pump is always energized. Odd that there is no separate pump only, boiler only and pump+boiler terminals on said Hive backplane. Is it me? (probably).
Thanks in advance.
Terry

 

[oldbutnotdead]

Could you have controlled hot water without heating with the old setup? Or was hot water on all the time & heating on demand?
You obviously have a grasp of what is needed, I'm not familiar with the Hive but I assume there are no volt free contacts (so you'll have L,N and maybe E then HEAT ON, HEAT OFF, DHW ON, DHW OFF?
Assuming that's the case you need a relay -240v coil, DPNO will do.
For hot water, live to the boiler goes to your DHW ON terminal.
For heating, live to the relay coil goes to your HEAT ON terminal.
You also connect permanent live (from the L supplying the Hive) to both COMMON terminals on your relay.
Finally you connect pump live to one of the NO terminals on the relay and boiler live to the other NO terminal on the relay.
Done.
Suitable relay here https://smile.amazon.co.uk/s?k=B08D...4H2&sprefix=b08dndqymr,aps,135&ref=nb_sb_noss , other suppliers exist.

PS Gravity hot water is a tad inefficient which is why no modern controllers will deal with it.

 

[Terry Williams]

When I moved in, there was a Potterton controller that did all the switching but didn’t do the remote control thing. Wish I hadn’t thrown it away.
When I drew the circuit out on a post it note it occurred to me that I need a relay to do the pump switching. I was hoping that since Hive clearly state that they can control HW and CH separately (using their dual channel receiver) that the standard wiring can actually do this. I might have been a bit too hopeful.
Many thanks for the response and suggested relay reference.
I wonder if we can get a Hive trained person to chip in. I’d hate to find out that one of the Hive terminals is suitable.
Terry

 

[oldbutnotdead]

The clue is Modern- I believe the 2 channel Hive can deal with most combinations of 2 and 3 port valves with no additions. Sticking a relay on the output doesn't remove any functionality from the Hive

 

[Johnmdc]

You don't need a relay.
The live feed to the boiler goes to terminal 3 and the feed to the pump goes to terminal 4.
You then need to set the Hive to "gravity mode".
To do this you press the left hand button on the Hive receiver for 5 seconds the top green light will change from green to blue to show that it is in gravity mode.
When in gravity mode of you select hot water just the boiler will fire up, if you select heating the boiler and the pump will run.

 

[Mottie]

Beat me to it.

 

[SUNRAY]

When I moved in, there was a Potterton controller that did all the switching but didn’t do the remote control thing. Wish I hadn’t thrown it away.
When I drew the circuit out on a post it note it occurred to me that I need a relay to do the pump switching. I was hoping that since Hive clearly state that they can control HW and CH separately (using their dual channel receiver) that the standard wiring can actually do this. I might have been a bit too hopeful.
Many thanks for the response and suggested relay reference.
I wonder if we can get a Hive trained person to chip in. I’d hate to find out that one of the Hive terminals is suitable.
Terry

I'm under the impression there is a 'gravity setting' in the hive, basically the hive either switches one output for hot water or both outputs for pumped heating. I don't know the details but I assume it's in the manual.

EDIT: I must learn to check for replies before posting. I started writing my reply then my daughter turned up for a chat

 

[winston1]

PS Gravity hot water is a tad inefficient which is why no modern controllers will deal with it.

Could you elaborate. Gravity hot water with the correct controls should be no less efficient than fully pumped. And you save the electricity for the pump.

 

[SUNRAY]

Could you elaborate. Gravity hot water with the correct controls should be no less efficient than fully pumped. And you save the electricity for the pump.

It depends on the pipe run. My first house I installed the cylinder virtually directly on top of the boiler with less than a 3m length of 28mm pipe. The speed of heating was phenominal but I had to add a valve to stop it overheating when the heating was running.

The house I'm in now, the cylinder was 2.4m above the boiler but offset by 3m using 22mm pipe. I was so used to the performance of the previous system I soon converted to fully pumped.

 

[ericmark]

There is a gravity setting with Hive, but there is no option to use a tank thermostat with standard Hive wiring, if you tried to include a tank thermostat it would turn off the boiler when DHW was hot enough even if rooms not hot enough.

 

[SUNRAY]

There is a gravity setting with Hive, but there is no option to use a tank thermostat with standard Hive wiring, if you tried to include a tank thermostat it would turn off the boiler when DHW was hot enough even if rooms not hot enough.

I'm assuming there is a thermostatic valve in place... However you've made me think about that and the simpleness of the advocated system would mean the boiler would be running and stopping on its internal thermostat.

 

[stem]

there is no option to use a tank thermostat with standard Hive wiring, if you tried to include a tank thermostat it would turn off the boiler when DHW was hot enough even if rooms not hot enough.

There is a way, I've done it using the NO and NC contacts in the cylinder thermostat to provide the electrical isolation between the boiler and the pump wiring....

Key:
Heating Live = Hive 4
Water Live = Hive 3

....the only downside is that whenever the CH is running, the hot water will still be being heated due to the plumbing restrictions of a 'gravity hot water' system. That's not so much of a concern because the boiler will be running anyway for the CH. However, when just the HW is 'on' the cylinder thermostat will stop the boiler firing unnecessarily once the HW cylinder is up to temperature.

 

[ericmark]

I use Nest not Hive, but also have a C plan boiler, since Nest has volt free change over contacts the wiring is very different, Com goes to boiler with Nest with no tank thermostat, and it can be configured to run with a tank thermostat.

But Hive uses internal programming so one output to pump, other output to boiler, and it runs both for central heating and only boiler for DHW.

The C Plan comes in three flavours, and over the years a tank thermostat has often been added so in summer it only runs boiler when required, and some times even a motorised valve on the DHW so the DHW temperature can be reduced to that used for central heating.

I have the basic design, and one advantage of Nest is in summer only heats DHW for 20 minutes 4 times a week, actually set to ½ hour, but boiler cuts out after 20 minutes, which is a great improvement from the old programmer which did not have a weekly program so heated water for at least an hour a day, well it would clearly turn boiler off as water heated up, but all pipe work also gets hot, so greater waste.

So basic with thermostat on tank with motorised valve and wired for Nest I in error for a long time thought Hive could not be used with C Plan, then I read how it was a software fix, I have looked for a Hive C Plan basic wiring diagram but can't find one, and wonder if the option has been removed? All I can find is

Gravity-fed and part-pumped systems are wired differently to standard boilers. With these, the hot water relay switches on the boiler, whilst the heating relay opens a valve, operates a pump, or both, to divert hot water
to the heating. If you are installing into a gravity-fed or part pumped system, complete the wiring and then switch the Hive receiver to ‘gravity-fed’ mode as follows:
1 Switch off the power to the boiler and receiver
2 Wait at least 5 seconds, then switch the boiler and receiver back on
3 Press and hold the hot water button for at least 10 seconds
The receiver status light will flash BLUE for 3 seconds when entering ‘gravity-fed’ mode. Or GREEN for ‘fully pumped’ mode. Fully pumped mode is the default for new devices.

I expected to find wiring diagram, however to be fair Nest do not publish a C Plan wiring diagram either. Also always know it as thermo syphon so calling it gravity fed may result in not finding results with internet hunt.

Just seen @stem wiring diagram, very good, just need 4 core cable then.

 

[Terry Williams]

You don't need a relay.
The live feed to the boiler goes to terminal 3 and the feed to the pump goes to terminal 4.
You then need to set the Hive to "gravity mode".
To do this you press the left hand button on the Hive receiver for 5 seconds the top green light will change from green to blue to show that it is in gravity mode.
When in gravity mode of you select hot water just the boiler will fire up, if you select heating the boiler and the pump will run.

Worked a treat. Many thanks. Nb the manual has no wiring info save the names given to the terminals which aren’t always helpful.

 

[ericmark]

Out of interest how well does it work, I have had two homes with thermo syphon. The first one if the pump was not run, then it would heat the DHW only, but if the pump ran once the water had started to flow radiators up-stairs would remain hot.

This house even without the pump running the radiators would heat up, but is a three story house, so had to fit motorised valves to stop radiators getting hot both due to DHW running and the other pump running, some one clearly thought with a flat under the house if they used two pumps one for house other for flat they could select what was heated, however with one pump turned off I got reverse flow.

I had thought with all electronic TRV's these would stop radiators getting hot, specially with micro-bore, but no, they did not get very hot, only just warm, but clearly wasting energy.

Talking to my boiler man it seems C Plan is very common with oil fired boilers, as it allows them to naturally cool by heating DHW, there is not run on to keep pumps running while the boiler cools, Y Plan also allows thermo syphon as default is DHW and water can still pass through a pump.