Central Heating randomly turning on when it should be off

[Jim]

Hi there,
First time posting so hope can be of assistance.
My central heating comprises a Baxi Duo-Tec Combi HE with a Honeywell Evohome Controller (latest Wifi version), wireless relay box (BDR91) and 6 Radiator Controllers (HR92).
The problem I am experiencing, since setting up, is that when the heating switches off at the set off time, the boiler then fires randomly up again anywhere between 5-15 minutes later, despite the Controller showing the correct “off” temperature that I have set at 10C for all the rooms. Room temperatures will still be in the region of 20C so there should be no need for the boiler to fire up. Also, ambient temperature where boiler is located is not low enough to trigger frost protection.
The boiler will then continue to cycle on/off every 5 minutes until I either push the reset button on the relay box or turn the boiler off then on again. The bathroom radiator does not have a thermostat and gets very hot during this so it appears the boiler is going into heat mode and not just the pump cycling. It seems to correct itself for a few days after a reset then starts playing up again until I reset the boiler by one of the two methods above.
Wondering is it more likely to be the boiler or the Evohome setup?
Any suggestions?
Thanks

[DBMandrake]

Do you have "Failsafe" mode enabled in the System Installer menu ?

Have you done a wireless signal strength test to all wireless devices and got a good result ?

When you bound the BDR91 did you clear any pre-existing bindings by holding down the button for 15+ seconds before holding it down for 5 seconds to bind ?

Have you seen any comms faults reported ?

[Jim]

Hi and thanks for your quick reply.
In response:
Failsafe is Disabled
Signal stength is good (ranging between 4-5) between the HR92s and the Controller. The Controller itself is situated 5 feet from the wireless relay box and with no obstructions and no loss of signal between the two.
All pre-existing bindings were cleared as outlined
No Comms faults being reported
Thanks

[The EVOHOME Shop]

Photos of the BDR91 would be handy.

[Jim]

Hi,
I've attached a photo below.
The BDR91 backplate is the original one used with a previous installation of a Honeywell CM927 Controller which was in the house when I moved in 3 years ago. I simply swapped out the fascia plate with the new one supplied with the Evohome controller as they use the same BDR91 Wireless Relay. As the previous system worked without fault this seemed logical rather than having to mess about with wiring which is as follows:
The black wire at N goes straight to the main Neutral supply to the boiler.
The first brown L goes to the Live out on the boiler.
The second brown L is a loop to terminal A.
The blue at terminal B goes to the switched live in terminal on the boiler.
image.jpg

I have noticed though, when taking the photo, that this wiring does not correspond to the diagram in the installation booklet, though as said above has worked without problem on the previous CM927. (The boiler requires a permanent live). Could this be the issue?
Hope this makes sense!

[The EVOHOME Shop]

I was actually after a picture of the BDR91 in position...

[Jim]

The picture shows the BDR91 in position, just with the front cover off. Nothing unusual about its positioning - mounted on a blank wall with no obstructions between Controlker or boiler.

[Cchris]

Not wanting to cloud the water here, but I had a similar problem with my old boiler, the problem being a faulty frost stat. The thing was firing up in the middle of summer when there was no demand. Could this be a possible issue?

[Jim]

Hi Ccris,
You could be right. I'm starting to realise it could be anything so thinking I'll just get the engineer out to give the system a once over.
Thanks

[SteveP]

Jim - you may find a posting I placed what may be a year ago (I lose track of the time) I had exactly the same problem with the system appearing to have a life of its own. I tried all the suggestions and then finally did a hard reset of the Evohome controller. All was well after that! I can only conclude that the software had become corrupted. No probs since then. Steve

[DBMandrake]

What do you consider a hard reset ? Do you mean a factory reset in the installer menu, removing the batteries, or both ?

[SteveP]

I did a factory reset and also left the batteries out for a couple of hours to clear any temporary memory.

[Jim]

I had already tried that as outlined and in addition cleared the binding on the Controller and BDR91 and rebound. Unfortunately this has not helped.
Thanks

[DBMandrake]

Very peculiar problem you have there with all the obvious things already checked. So a bit of blue sky thinking:

Do you have the new Wifi model firmware that reports local HR92 overrides back to the Evotouch ? You can check this by going into settings and holding down Device Settings for about 20 seconds. If you have the new version Application Software version will say 01.00.02.01. Or just try adjusting an HR92 directly then check if it reports the change back to the main controller.

If you do not have this new version yet, it is possible that one of your HR92's has been manually turned up by somebody else in the house without your knowledge. On the older firmware this will not be indicated on the main controller (or smartphone app) but will cause the boiler to come on, even if the evohome controller is in "OFF" mode.

When the boiler is coming on unexpectedly have you manually been around to every HR92 in the house and checked that the set point is at least 2 degrees below the current room temperature ? And that every radiator is cold or at least not flowing ?

Another forum member had a similar problem to you which turned out to be that a guest had turned up the HR92 in the guest bed room, and because there were no scheduled temperature changes for that zone the HR92 had remained at the elevated set point which was never communicated back to the controller, so only manually checking the HR92 found the issue.

Is it possible there are guests or children in the house who may be fiddling with their HR92's without your knowledge ? (It is possible to lock the controls on specific HR92's so they can only be controlled via the controller or phone apps if you have any suspected fiddle fingers in the house )

Also you say it was turning on in 5 minute cycles - the default cycle time is actually 10 minutes (6 firings per hour, set in the installer menu) which means it should only fire once per 10 minute period. If you can't find any other cause can you time how long it fires in each 10 minute cycle ?

Also in response to a comment in your original post where you said pushing the button on the BRD91 "reset" it, that is actually only a temporary override, not a reset. It will turn the relay off if it is on, or on if it is off, but at the next scheduled TPI switch time it will resume where it left off. So if it is modulating the boiler on and off in TPI mode it will come back on again a few minutes later.

[The EVOHOME Shop]

I had already tried that as outlined and in addition cleared the binding on the Controller and BDR91 and rebound. Unfortunately this has not helped.
Thanks

When you rebound the BDR91 what process did you take?

I suggest the following which is how I rebind them:

Set 'BOILER CONTROL' to 'NONE' under 'SYSTEM DEVICES'
Exit the 'INSTALLATION MENU'
Reboot the evohome Controller by removing or parting batteries for a couple of minutes.
Go back into the 'INSTALLATION MENU' then 'SYSTEM DEVICES' again
Press 'BOILER CONTROL' and select 'WIRELESS RELAY BOX'
Then rebind the BDR91 using information on Page 18 of the Installation Guide - make sure you have 1-2 meters minimum between the evohome Controller and the BDR91 when you bind them and when you get the 'SUCCESS' message on the screen wait a minute or two before pressing the green tick.

If this doesn't work start checking the installation of your HR92's, including RF checks detailed on Page 31.