Honeywell evohome and megaflow

[philfraemohs]

hi guys, just wired up a Honeywell evo crontroller with a relay for the heating, a tank stat and a relay for the hot water, I managed to get it working after a lot of messing around, the problem is it's a megaflow hot water tank and I have disconnected the megaflow tank stat which has a overheat thermostat I think, (there was 3 connections) I think the overheat thermostat is supposed to stay but dunno how to connect it up. Theres a 3 port valve for heating and hot water and another hot water valve(which is on the hot water side and just connected straight to the switch live to boiler)
I haven't got any experience with megaflow

 

[Leesparkykent]

Are you using the wireless cylinder thermostat?

 

[philfraemohs]

Yeah, the wireless relay came with tank stat probe which I replaced the mega flow one with

 

[Leesparkykent]

Yeah, the wireless relay came with tank stat probe which I replaced the mega flow one with

you'll have to forgive me as not overly familiar with the evo home. Does the wireless cylinder thermostat communicate to a relay BDR91 which the valve is connected to?

 

[philfraemohs]

Yeah the cylinder probe connects to a wireless cylinder thermostat transceiver which then wirelessly connects to the bdr91 relay

 

[Leesparkykent]

okay so you also need to wire the high limit thermostat of the megaflow in series with the interlock two port valve which should be sited between the cylinder and port b of the three port valve as this is an important safety feature that will stop the cylinder from exploding if the temperature thermostat sticks/goes faulty or three port valve lets by.

If you've removed the temperature probe/thermostat from the megaflow and inserted the temp probe from the evo home hotwater kit you should still have the high limit thermostat which is normally closed and opens on temperature rise.

The grey from the three port connect to terminal C on BDR91, link live to A on BDR91, B on BDR91 connect to one side of the high limit thermostat on mega flow and from other side of high limit thermostat on mega flow connect to brown of the two port valve.

Grey of the two port connect to permanent live and orange of the two port to switch live of the boiler.

 

[philfraemohs]

Thanks mate I'll have a go at that

 

[Leesparkykent]

I've looked at megaflow wiring diagrams and it shows the cut out going back to dhw off on the programmer, but I have now disconnected the programmer cause the eco controller is now the programmer

on the megaflow there are two thermostats one is temperature control the other is a high limit thermostat these are connected in series internally. DHW off from programmer, the grey from the three port and normally open on the megaflow would usually be connected together if it was a conventional set up. As its not a conventional set up due to using the evo home kit you need to change it around slightly. So when the hot water is not set to come on, on the controller or its satisfied because its up to temperature then by connecting the grey of the three port to terminal C off the BDR91 achieves the same thing which allows the three port to move over to heating only if required.

 

[Leesparkykent]

Just thinking is there another dry pocket about 1/3 of the way up on the cylinder that the evo home hot water probe could be put in?

 

[philfraemohs]

The megaflow cylinder stat/override is all built in one and has connections 1 , 2 & 3. Any ideas which numbers I have to wire into, not sure which one does the normal thermostat and which ones are the override and have no instructions or diagrams

 

[Leesparkykent]

The megaflow cylinder stat/override is all built in one and has connections 1 , 2 & 3. Any ideas which numbers I have to wire into, not sure which one does the normal thermostat and which ones are the override and have no instructions or diagrams

1 and 2 but you will have to turn the thermostat all the way up on the megaflo because you want the evohome temperature probe/thermostat to do the work.

 

[stroud repairs]

okay so you also need to wire the high limit thermostat of the megaflow in series with the interlock two port valve which should be sited between the cylinder and port b of the three port valve as this is an important safety feature that will stop the cylinder from exploding if the temperature thermostat sticks/goes faulty or three port valve lets by.

If you've removed the temperature probe/thermostat from the megaflow and inserted the temp probe from the evo home hotwater kit you should still have the high limit thermostat which is normally closed and opens on temperature rise.

The grey from the three port connect to terminal C on BDR91, link live to A on BDR91, B on BDR91 connect to one side of the high limit thermostat on mega flow and from other side of high limit thermostat on mega flow connect to brown of the two port valve.

Grey of the two port connect to permanent live and orange of the two port to switch live of the boiler.

That makes a lot of sense and will help many others so thank you for taking the time.

To simplify matters further- if the megaflow has been wired with the supplied wiring centre then there is actually nothing to change other than (and please check this) to remove the third connection of the "megaflow eco indirect thermal controls" -terminal No 3 from term 11 of the wiring centre.?
(and of course link out the room thermostat

I have proved that the high limit thermos does indeed break contact on pins 1 and two (13 and 14 of the supplied wiring centre) but what does the third connection do and am I right to isolate it?

image of adapted wiring diagram uploaded three times sorry.