The Efficient Home Forum

Hello,
I’m looking for some feedback on how evohome would work in my property. I’ll start by listing what we have at the moment.

• A Thermecon oil fired system boiler in our garage
• A MegaFlo 210i unvented cylinder in an airing cupboard.
• The system is plumbed as Y-plan but with an additional two port valve acting as overheat protection for the cylinder as documented here https://www.flameport.com/electric/cent ... ntedHW.cs4
• The airing cupboard contains the three port and two port valves, the wiring panel, system programmer (a Sunvic RF one with the thermostat downstairs). Two three core cables are routed from the garage to the airing cupboard, one brings mains power to the wiring panel and the second takes power back to the boiler.
• The house is an extended four bedroom detached house which currently has 15 radiators in it.

Moving to what I think I need.

The evohome system looks to give us the control we need over our heating and one of tehvalue packs looks like it will be a good starter with a few extra HR91/2s.
I don’t think all of the radiators need smart valves. The utility room, for example is barely used and could just have a normal TRV and it’ll get warmed up as and when the system fires up for other demands
By thinking carefully I think I can get to fewer than 12 zones but with some zones having more than one radiator in. I believe that evohome supports this.
My current TRVS are a fix of Drayton RT212s and Westherm 4s. I believe the latter will require adapters.
Questions I have.

• I read that the BDR91s need to be 300mm from everything metal. The most obvious place for them is in the airing cupboard but that is a mass of metal as it contains cylinder, valves and pipework. If I mount them high up on the wall of the airing cupboard on opposite walls is that likely to work OK or will the metalwork between the BDR91s and the controller (which will be downstairs) be an issue?
• Do I have to use the CS92A if I want to control the hot water? Is it possible to use the DHW BDR91 with the existing cylinder thermostat? I realise that this wouldn’t allow evohome to control the hot water temperature, it would only act as a timer.
• Is there a sample wiring diagram for setting up a Y-plan plus two port overheat valve system? I think I can see how to do it but I’d appreciate it if there is a known good way.
• For a room with two radiators in, is it possible to have one HR91 and one HR92 as the temperature could be overridden by the one HR92?

Many thanks in advance
Chris

Wiltshire Chris wrote:Hello,
I’m looking for some feedback on how evohome would work in my property. I’ll start by listing what we have at the moment.

• A Thermecon oil fired system boiler in our garage
• A MegaFlo 210i unvented cylinder in an airing cupboard.
• The system is plumbed as Y-plan but with an additional two port valve acting as overheat protection for the cylinder as documented here https://www.flameport.com/electric/cent ... ntedHW.cs4
• The airing cupboard contains the three port and two port valves, the wiring panel, system programmer (a Sunvic RF one with the thermostat downstairs). Two three core cables are routed from the garage to the airing cupboard, one brings mains power to the wiring panel and the second takes power back to the boiler.
• The house is an extended four bedroom detached house which currently has 15 radiators in it.

Moving to what I think I need.

The evohome system looks to give us the control we need over our heating and one of tehvalue packs looks like it will be a good starter with a few extra HR91/2s.
I don’t think all of the radiators need smart valves. The utility room, for example is barely used and could just have a normal TRV and it’ll get warmed up as and when the system fires up for other demands
By thinking carefully I think I can get to fewer than 12 zones but with some zones having more than one radiator in. I believe that evohome supports this.
My current TRVS are a fix of Drayton RT212s and Westherm 4s. I believe the latter will require adapters.
Questions I have.

• I read that the BDR91s need to be 300mm from everything metal. The most obvious place for them is in the airing cupboard but that is a mass of metal as it contains cylinder, valves and pipework. If I mount them high up on the wall of the airing cupboard on opposite walls is that likely to work OK or will the metalwork between the BDR91s and the controller (which will be downstairs) be an issue?
• Do I have to use the CS92A if I want to control the hot water? Is it possible to use the DHW BDR91 with the existing cylinder thermostat? I realise that this wouldn’t allow evohome to control the hot water temperature, it would only act as a timer.
• Is there a sample wiring diagram for setting up a Y-plan plus two port overheat valve system? I think I can see how to do it but I’d appreciate it if there is a known good way.
• For a room with two radiators in, is it possible to have one HR91 and one HR92 as the temperature could be overridden by the one HR92?

Many thanks in advance
Chris

Hi Chris,

All evohome system schematics and wiring diagrams are in the back of the evohome Installation Guide, which can be downloaded from here this page - https://theevohomeshop.co.uk/content/11 ... help-guide

300mm minimum is the recommended from metal and other evohome devices, to ensure the system works correctly. Anything metal in the line of RF will hinder performance, as per the previous link I posted.

The CS92A is essential, so not something you can setup evohome to do hot water without. evohome doesn't have the facility for timers, its time and temperature or nothing.

If you have a room with multiple HR91/HR92, personally I stick a thermostat in there as a zone sensor (T87RF or DTS92E) which accurately represents the air temperature. This is also then your override for the entire zone too.

I think that answers your questions. If you have anything else, maybe give us an email or call Monday?

Thanks,

Richard

Hi Richard,
Thanks for your reply. Sadly, the evohome guide doesn't cover the set up where a Y-plan system has an extra two port valve on the hot water feed which is there to prevent the cylinder over-heating.
I've had a go at modifying the wiring diagram for the standard Y-plan. What I've gone for is

• Instead of taking the wire from the B terminal of the DHW BDR91 I take that into terminal 1 of the MegaFlo thermal controls.
• I then take the output from terminal 2 of the MegaFlo terminal controls to the Brown cable on the two port valve. I believe terminal 2 is live when the cylinder temperature is below the thermostat level.
• I then take the Orange cable from the two port valve and send that to the boiler live.

So, in the case that the cyclinder is cold then the two port valve should open and then send live down the orange wire to the boiler. On the other hand if the cyclinder is over the temperature set on the cyclinder thermostat (the built-in MegaFlo one) then power won't go to the two port valve and so the spring will close the valve.

In their documentation, MegaFlo say that for regulations to be met their thermostat has to stay in place. I've based my changes on this technical note:
https://ensupport.getconnected.honeywel ... uage=en_US

Here's my revised diagram. In reality I'd use the terminal block to connect the components rather than wires going direct from component to component.

Does this seem correct to you?


Thanks again
Chris

Yep seems fine that Chris.

Sorry for the late reply.

Thank you