Is the fundamental design of Evohome Flawed?

[Cyclobob]

I have had this problem recurring since I installed as I see a number of others had. The problem is that when the HW relay is activated, the CH relay fires up. The solution usually is to make sure the system is configured correctly and the BDR91's are not close to each other nor large metal objects as these issues can cause wireless interference. But I have tried all the recommended solutions and it still happens from time to time creating system noise as the ABV comes into operation. The reason I think the design is flawed is that I have spent all my career in networking and when designing systems like this you other use a two way protocol or ensure that binding is totally secure and unique. Evohome seems to send out a regular ON signal to the BDR91's because I can turn of the CH one manually, but a minute or so later it comes back on why couldn't it send an ON signal to the HW followed by an OFF to the CH, that way if there was any interference at least it would be countered (but if the system is this flaky, the the HW might also go off). IMHO Honeywell need to make the protocol much more robust and immune to typical system noise and installation issues.

Bob

[Richard]

Hi Bob,

Welcome to the forum.

IMHO, it is not the system that is flawed but understanding of central heating design and how the evohome system works with different systems is mostly to blame.

In the case where the 'heating' valve BDR91 comes on at the same time as the 'hot water' valve BDR91, this is just a misunderstanding of the correct configuration. Using a 'boiler control' relay setup for an S Plan or Y Plan system will mean the heating valve will of course come on at the same time as any demand on the evohome system. Correctly configuring the system without a 'boiler control' relay via hot water guided configuration will mean this problem would not exist.

There are always improvements that can be made to any system design, however for the majority of evohome systems out there with correct installation and setup means these systems do work perfectly without fault.

[Cyclobob]

Are you saying that if you have an S plan with independent valves for the HW and CH that you only need one BDR91? That cannot be correct because the HW BDR91 controlling the HW valve would not be able to open the CH Valve. So the CH valve has to have a BDR91 fitted to it in order for the controller to send a signal to open it and turn the boiler on. It therefore has to be configured in the controller. I understand what you are saying about controller config, but having been through every option and factory defaulting several times I still get the issue. The annoying thing is that both don't come on all the time. Without fail both come on in the morning, I can manually turn off the CH valve, but it comes back on in the next few mins. Yet later in the day if there is a HW demand, only the HW valve comes on. All rads are set to 5 degrees in the morning and the heating is set to off anyway. Both BDR91's are 600mm from the cylinder and they are over 300mm apart, I will move them further apart this weekend. So it is not a config error more an issue with wireless saturation, which should not happen with proper system design (having spent 40 years in communication systems design including spells at Nokia and Vodafone, I know a bit about robust wireless system design). If the BDR91 talks back to the controller, the controller should always set it's state to what it should be or flag errors.

Thanks for the reply

Bob

[Cyclobob]

My set up is exactly as shown on P.42 of the Evohome installation guide which shows a BDR91 connected to each zone valve. When either of the zone valves open the boiler is turned on. However, in our system as no HR92's are open and the CH BDR91 comes on randomly, the flow is dumped through the ABV which causes noise and pressure that shouldn't happen.

Bob

[Richard]

Hi Bob,

Thanks for the emails and forum posts.

This is a definitive area of confusion, hence we are trying to take the technical away from my EVO-Help page and bring it here where it can be discussed and resolved with the relevant details.

In an S Plan system, you are not controlling a boiler (well you are but indirectly through the motorised zone valve end switches), hence you leave the 'BOILER CONTROL' set to 'NONE' and then bind both the heating and hot water zone valve BDR91 Wireless Relay Boxes through 'GUIDED CONFIGURATION' > 'STORED HOT WATER CONFIGURATION' ensuring you choose '2 TWO PORT OR THREE PORT VALVES' option when prompted.

I have done a video here to back this method up - https://youtu.be/UtbIt1oxe3I

I hope that helps.

[Cyclobob]

Many thanks Richard, I resolved my issues this weekend. I never expected that the heating actuator would be configured in the Stored Hot Water settings. This is not well described in the Installation guide, nor the online training. Thankfully you have put this forum together and the excellent video you posted on this subject. Very happy with my Evohome now!

Bob

[Richard]

Great stuff Bob, glad all is resolved! If there is anything else, please let me know.