Honeywell Evohome - Wiring with Hot Water Cylinder

[antsals]

Because everyone on here is more helpful than Honeywell I have another very quick question. This maybe dumb but I wanted to make sure I understand what can or can't be done.

Sensiableheatuk has already answered a couple of my questions (thanks again) did'nt want to keep pestering you.

Here's my question.......going through the wiring diagram for the Evohome Sundial package, my system is currently configured in a Y-Plan.

I'm also changing my hot water tank to a Unvented, Indirect, Mains Pressured with Solar coil tank. I've not yet decided which tank I will purchase but for some reason I have a liking to the Megaflo Eco Solar, http://www.heatraesadia.com/365.htm

But this is where my question comes in, the thermostat seems built into the tank and the wiring diagrams seem very different (attached) is it possiable to wire the thermostat directly to the CS92A unit and not use the honeywell thermostat? Has anyone wired one of these types of tank before with the Evohome unit?

Cheers
Ant

[listuk]

We put in a evohome last year and spoke directly to honeywell who said it would not support our megaflow (or any unvented system).

So we ended up using a simple Siemens RWB2 which we already has to control the evohome.

To be honest I'm glad we did, we have had a number of issues with the evohome from signal problems to CH not coming on as expected. At least the hot water system works without fail.

[TonySmith]

Out of interest, do you know why that would be? I was wondering about combining Evohome with an existing conventional cylinder thermostat, simply because the wireless stat is so ridiculously expensive. Obviously I could install independent DHW controls, but that would remove some of the point of an integrated system

We put in a evohome last year and spoke directly to honeywell who said it would not support our megaflow (or any unvented system)

[listuk]

Out of interest, do you know why that would be? I was wondering about combining Evohome with an existing conventional cylinder thermostat, simply because the wireless stat is so ridiculously expensive. Obviously I could install independent DHW controls, but that would remove some of the point of an integrated system

i think the answer to that is evohome has no physical inputs, it can only communicate wirelessly with approved products. so you could not physically wire your existing thermostat into the evohome.

[SensibleHeatUK]

There is no option to the wireless stat for hot water control - you cannot bind the BRD91 relay to the hot water channel without also binding the CS92A wireless HWS sensor. Evo simply has no support for time-only relay control - we've been asking Honeywell for this as we use a lot of time-only channels on the majority of our Hometronic installations. AFAIK there are no further planned updates by Honeywell for the existing Evo platform.

Regarding the issue over unvented cylinders, that is because Honeywell only supply their standard strap-on sensor unit (just like the wired CS92 stat) that is used on standard uninsulated copper cylinders. The problem is that Megaflow and similar cylinders are factory insulated with an out metal or plastic jacket covering the insulation. Therefore you would have to cut into this to expose the cylinder wall and then find some way of securing the sensor in place. Not a great idea!

The other option is to use a replacement sensor element with the same properties as the Honeywell version, that can fit inside an existing pocket in the cylinder but not all cylinders have these either. After that you simply wire the Evo relay in series with the existing thermostat, and set the existing thermostat to a higher level than you use with Evo to ensure that Evo has overall control but you retain the existing control/high-limit thermostat as it is an integral safety device. Of course you'll not get help in finding replacement sensors from Honeywell as it simply adds another support issue to their already over-stretched UK support team.

[TonySmith]

Thanks. Regarding your last comment, does that mean that Evo is on its way out? Shame as I think it would work quite well for us, assuming it would fit our TRVs of course.

There is no option to the wireless stat for hot water control - you cannot bind the BRD91 relay to the hot water channel without also binding the CS92A wireless HWS sensor. Evo simply has no support for time-only relay control - we've been asking Honeywell for this as we use a lot of time-only channels on the majority of our Hometronic installations. AFAIK there are no further planned updates by Honeywell for the existing Evo platform.

[TonySmith]

I understand that, but I was hoping I could just wire the thermostat in series with the BDR91 outputs, so I'd have wireless ON/OFF from the Evo but using local temp control. Apparently you can't do this. Actually for my installation the whole wireless thing pushes the costs right up for no particular benefit. I've got my zone valves fitted (CH and DHW) and both of these, the pump, and the boiler are all within easy wiring distance. The only thing that will really benefit from wireless will be the HR80s or remote room sensors.

i think the answer to that is evohome has no physical inputs, it can only communicate wirelessly with approved products. so you could not physically wire your existing thermostat into the evohome.

[SensibleHeatUK]

Thanks. Regarding your last comment, does that mean that Evo is on its way out? Shame as I think it would work quite well for us, assuming it would fit our TRVs of course.

Certainly not on the way out, just more likely that the UK can only change it slightly as its a euro-wide product, so unless the majority of territories needed the feature then it was not likely to happen.

Compare it to Hometronic which has now been around for more than 10 years, so I'd certainly expect it to stay around for a long time yet :-)