Evohome questions before blowing my budget....

[holybob]

OK, having done lots of research around the best multizone smart heating system to go for, I'm making the plunge for Evohome.

Current system: Worcester Boiler, unvented DHW tank, 3 x CH zones (don't ask, crazy implementation due to an extension we had).
18 x rads, ideally I want 14 Evohome zones but 12 will suffice to make life easy (I'll combine the kids' bedrooms). All rads except 1 per zone have TRVs. Heating and DHW was originally controlled using a ChannelPlus H47XL with 'dumb' thermostats in three areas of the house. The H47XL is still there, all zones constantly 'on', but the thermostats were replaced by (slightly) intelligent ones which control scheduling etc.

Will moving to Evohome pose a challenge for me because I have three zones? I want these all combinined to one big 'master' zone and then 12 'virtual' (Evohome) zones. Can I just wire all three zones together (so they're either all on or all off)? Assuming I can, I think I need the following shopping list:

1 x ATP921R3100 - starter kit (controller, plus BDR91)
18 x HR924UK
1 x ATF500DHW

Is that everything?
Will the BDR91 sit in place of the H47XL?
Can I just remove the three thermostats and blank them off? (i.e. they're now surely totally redundant)
For the rads which currently have no TRVs, with Evohome am I ok to put on the HR924UKs so EVERY rad in the house is smart?
If I wanted to have 14 zones, would I 'just' need another controller?

Thanks in advance, obviously 18 x TRVs hikes the price up but I want to go the whole hog (don't understand the point of not doing it properly) - I just want to make sure I've left no stone uncovered before proceeding. I'll probably get my friendly Spark to fit it but I think it'll be the first Evohome he's done.

Gavin

[DBMandrake]

Current system: Worcester Boiler, unvented DHW tank, 3 x CH zones (don't ask, crazy implementation due to an extension we had).
18 x rads, ideally I want 14 Evohome zones but 12 will suffice to make life easy (I'll combine the kids' bedrooms).

If you combine the kids bedrooms (I assume you mean three bedrooms, to save on two zones ?) then as long as you set the zone to be a "multi-room" zone, it will work fine. They will all share the same schedule but they will each measure their own room temperature at their own radiators so work independently to maintain the same temperature in each room. (A standard single room zone with multiple HR92's only uses a single temperature sensor which naturally isn't workable across separate rooms)

The control panel will only be able to display the temperature of one of those three rooms, the other two will not be visible except on the HR92's themselves if you have them set to room temperature display mode. (The other two will be able to call for heat though) If you make a manual override to the zone via the controller or phone app it will apply to all three rooms. If you override the temperature by turning the dial on one of the three HR92's it will override only that one room and only until the next scheduled set point. In a multi-room zone any override made directly at an HR92 will not be displayed on the control panel however.

Will moving to Evohome pose a challenge for me because I have three zones? I want these all combinined to one big 'master' zone and then 12 'virtual' (Evohome) zones. Can I just wire all three zones together (so they're either all on or all off)?

Yes, assuming the cables for the three zone valves all come back to the same place (your wiring centre) then you can just wire all three of them in parallel to be controlled by one BDR91 and they will switch together in unison. The HR92's themselves will provide the zoning on an individual room basis, so effectively having three heating zone valves is redundant, but not an issue as they will just open and close together with HR92's having final authority on which rooms are being heated.

Assuming I can, I think I need the following shopping list:

1 x ATP921R3100 - starter kit (controller, plus BDR91)
18 x HR924UK
1 x ATF500DHW

Is that everything?
Will the BDR91 sit in place of the H47XL?

If the H47XL controls both heating and hot water zone valves, then it would have two relays inside it, and this would be replaced by two BDR91's, (spaced at least 30cm apart for wireless signal reasons) one for the heating zone valve(s) and one for the hot water zone valve. You get a BDR91 in the starter kit and another one in the hot water kit so you will get two. BDR91's are a simple SPDT (single pole double throw) volt free relay that can supply up to 3 amps and can be used either at 240v AC or at low voltages as required.

In this two relay scenario you would rely on the switch inside the hot water and heating zone valve relays to fire the boiler - this is probably how your system is wired now but you might want to check. As an alternative you can have a third BDR91 which acts only as a boiler control relay which is wired directly to the boiler - this is the configuration I have at home.

The hot water kit comes with a strap on sensor for vented and an insertion sensor for unvented - so there needs to be a pocket about 1/3rd of the way up the cylinder that will accept the sensor, and this needs to be in addition to the safety cutout sensors for an unvented cylinder that needs to remain in service as well.

Can I just remove the three thermostats and blank them off? (i.e. they're now surely totally redundant)

Presumably they are wired in series with each heating zone valve - in which case yes, you would remove them. You'd either need to bypass them in the wall box or disconnect the wiring and bypass it elsewhere.

For the rads which currently have no TRVs, with Evohome am I ok to put on the HR924UKs so EVERY rad in the house is smart?

You can put HR92's on every radiator in the house if you want (that's what I have) provided that there is an automatic bypass valve installed in the system - before the heating zone valves, so that there is somewhere for the boiler flow to circulate in the event that all HR92's are closed, which can happen for a short time such as during boiler overrun when the system is shut down.

If I wanted to have 14 zones, would I 'just' need another controller?

Sort of. It's basically a whole separate system which means you'd have to duplicate the heating zone valve relay (you'd have another BDR91 belonging to the second unit for the heating zone valve) and you could only control some zones from one controller and some from the other. There would be no house-wide modes such as away - you'd have to put both into away mode etc.

Personally if you're only two zones over the limit I'd work to consolidate some less critical zones like hallways or zones that can share schedules using multi-room zones rather than go the two controller route.

Thanks in advance, obviously 18 x TRVs hikes the price up but I want to go the whole hog (don't understand the point of not doing it properly) - I just want to make sure I've left no stone uncovered before proceeding. I'll probably get my friendly Spark to fit it but I think it'll be the first Evohome he's done.

That's certainly a big purchase - I have 9 TRV's in my system and I built it up over time. So best to get some other opinions as well in case I've missed something or got something wrong.

[paulockenden]

First thing to do, I reckon, is a comms check. Sounds like you have a large-ish property, and others have had problems with extensions etc.

You'll either need a friendly/knowledgeable installer for this, or else buy a controller and an HR92 from a supplier such as Amazon that has a friendly returns policy!

P.

[holybob]

Thanks both. I think that answers my questions pretty much perfectly, and I think a single-controller system is definitely the way to go. Some of the boiler stuff is over my head but I'll consult my fitter (who installed the original system) on all that.

18 x TRVs sounds a lot but I can get 4 for £180 at the moment. The house isn't crazy big - A northern end terrace with a double-storey side extension so no palatial mansion here unfortunately :-)

[PaulGr]

My 2 pence worth...

I suggest you get your evohome kit from a knowledgable supplier who can give you support when things go wrong! Don't be tempted to save a few quid by getting it from the likes of Amazon or Screwfix. I can highly recommend Richard at The Evohome Shop.

You should definitely fit an Automatic Bypass Valve. Having one uncontrolled radiator (such as a bathroom towel rail) may not give sufficient flow rate for your boiler.

Paul O makes a good point about a comms check. The Evohome Shop sells a comms check kit. It may be worth buying it. Also, I suggest you read the articles about BDR91 and evotouch siting on the Evohome Shop's forum. Use a cable finder to check for hidden cables where you plan to locate the evotouch controller. Also, bear in mind what is on the other side of the wall.

What make are your existing manual TRVs? If they are generic Chinese ones, consider replacing them with Honeywell Valencia TRVs. My system had cheap Chinese TRVs and I had problems with one radiator not turning on and another not turning off fully. It turned out the valves all had different pin heights. I replaced them and the problems went away.

Consider using a thermostat such as the DTS92 in your living room. I have mine on a coffee table. That way I can control the temperature at where I sit.

Hope this helps.

[holybob]

I suggest you get your evohome kit from a knowledgable supplier who can give you support when things go wrong! Don't be tempted to save a few quid by getting it from the likes of Amazon or Screwfix. I can highly recommend Richard at The Evohome Shop.

Hmm... So here's the thing. I work for Honeywell (totally different division to Evohome) and originally started this journey thinking I could get a nice little staff discount.... Not so though. But then I discovered the HR92s online for £179.99 for a pack of 4, and saw the controller kits on eBay for around £100 (yes, I know now to make sure they're the latest model!!!!). So the barrier to entry was coming down. And I thought it'd be simple to install (I'm no spark but have done wiring in my time, I'm certainly no plumber though and wouldn't go near that side!). I assumed I'd replace the TRVs, switch out the current Horstmann ChannelPlus programmer for the BDR91 (plus now I know a second BDR91 for the water) and life would be good. And I could enlist the guy who fitted my current heating if needed. But now I'm a bit more scared.... And getting in the pros to do it bumps the cost meaning I'll probably not actually do it.

Paul O makes a good point about a comms check. The Evohome Shop sells a comms check kit. It may be worth buying it. Also, I suggest you read the articles about BDR91 and evotouch siting on the Evohome Shop's forum. Use a cable finder to check for hidden cables where you plan to locate the evotouch controller. Also, bear in mind what is on the other side of the wall.

Cables are no problem -. I know the house's wiring backwards. The BDR91(s) would be very central within the property so until you said that, I'd have had no concerns about comms... but now I do.... although I can't find the comms check kit on EvoHomeshop?

What make are your existing manual TRVs? If they are generic Chinese ones, consider replacing them with Honeywell Valencia TRVs. My system had cheap Chinese TRVs and I had problems with one radiator not turning on and another not turning off fully. It turned out the valves all had different pin heights. I replaced them and the problems went away.

Not actually a bad point. They're the ones which came at the time of install. Quality feels OK but they're unbranded.... However surely this is a moot point if I'm replacing all with HR92s?

Consider using a thermostat such as the DTS92 in your living room. I have mine on a coffee table. That way I can control the temperature at where I sit.

I was already going to do that. The main lounge TRV is behind the back of the sofa so temp measurements will be off in that room :-)

Thanks again all.....

[PaulGr]

Gavin, some comments on your reply.

Perhaps just get some of your evohome kit from a knowledgable supplier and say the bulk of your HR92s from a cheaper source. That way you should still be able to get support.

The comms check kit is on this page: https://theevohomeshop.co.uk/13-honeywell-evohome . It's called a Honeywell evohome Wireless Signal Strength Test Kit.

The evotouch controller and BDR91 can be sensitive to nearby electrical and electronic equipment, hence the siting and spacing recommendations. Cordless phone base stations apparently are notorious for causing evohome comms problems.

When you buy HR92s you only get the electronic TRV head, not the valve body. My problem was that the Chinese valve bodies all had different pin heights.

Paul

[holybob]

Great answers, and great suggestions. I'll definitely get the test kit for a day to put it through it's paces!

[jvallis]

You should definitely fit an Automatic Bypass Valve. Having one uncontrolled radiator (such as a bathroom towel rail) may not give sufficient flow rate for your boiler.

This is fairly important - without an ABV, I strongly suggest making 2-3 of your towel rads to be uncontrolled. This will mean you'll get a warm bum whenever any heat is called anywhere in the house (no bad thing, if you remember Bakelite seats), but at least water can circulate if the boiler happens to be on and all the radiators are off.

Also, which Worcester Bosch boiler do you have? You could potentially get another device (Nefit?) to attach to the boiler and use the OpenTherm gateway. This effectively 'feathers the accelerator' of the boiler, rather than mashing it to the metal every time you need heat - definitely worth investigating if you can.

[DBMandrake]

This is fairly important - without an ABV, I strongly suggest making 2-3 of your towel rads to be uncontrolled. This will mean you'll get a warm bum whenever any heat is called anywhere in the house (no bad thing, if you remember Bakelite seats), but at least water can circulate if the boiler happens to be on and all the radiators are off.

Towel rails are not useful as bypass radiators if they are after the heating zone valve(s). Otherwise there is no bypass when the zone valves are closed during say pump overrun.

If all radiators are after heating zone valves (which is probably the case) there must be an automatic bypass valve installed before the zone valves. Chances are it's already there.