Problems replacing Honeywell CM927, ST9400C and BDR91 with Wireless Tado X receiver and termostat

Malcolm_J

Hello,

I have a Vaillant Vitodens 100-W WB1C boiler with hot water tank. The bolier serves a single zone of radiators and heats up the hot water tank.

The oroginal controller setup was a wireless Honeywell CM927 thermostat connecting via a Honeywell BDR91 receiver for the heating control, and the Honeywell ST9400C to control the hot water tank schedule.

I followed the installation instructions for replacing the ST9400C with the Wireless Receiver X and all seemed good. Radiators heating up nicely. Took the batteries out of the CM927 and went to bed.

In the morning, the hot water tank had been heated, but the radiators were cold. I pressed the over-ride button on the BDR91 receiver and the heating came on.

I have looked at the procedure for replacing the BDR91 with the Wireless Receiver X but stopped as I'm unsure how to proceed. The instructions tell me to connect the L and N wires from the BD91 to the Tado receiver, but I'm concerneed that it will cause a short circuit. The A and B wires from the BDR91 are to go to the CH COM and CH NO terminals respectoively in the receivver. These are already connected and bridged per the instructions for replacing the ST9400C. I have left the BDR91 untouched for now, apart from labelling up the wires.

After the initial installation I had the Hot Water tile visible on the App. Now, it's gone.

It seems that the Tado system is not controlling the boiler at all. If I turn off all heating, nothing happens. I'm having to use my immersion heater to heat the hot water.

I wondered about removing the wiring done for replacing the ST9400 (which only controlled the hot water schedule) and replacing it with the suggested wiroing for the BDR91, leaving the hot water connections in place.

I also had to reset the Tado wireless receiver X as it was showing LEDs indicating it had lost connection to WiFi. It now shows 3 WiFi LEDS and the app shows it as connected, but the Hot Water tile is not in the app.

Note: the large white box next to the towels is a Solar iBoost immersion heater controller.

Any advice on how to proceed will be very welcome.

wateroakley

@Malcolm_J Hello. From the description and pictures, this appears to be a wiring problem. Hard to tell which wire is which in the rats nest box. However … in the BDR91 receiver, the relay connection wires on A and B would usually be linked with a Wago connector from the Tado starter kit. Taking the batteries out of of the Honeywell CM927 thermostat will undoubtedly result in 'no heating'. If the Hot Water icon has disappeared from the Tado App, it's likely that the wireless receiver is probably in 'combi' mode and needs resetting to S-Plan.

Malcolm_J

Thanks for the reply. I reset the wireless receiver to S/Y plan and now the Hot Water tile is showing in the app.

I also connected the A & B wires inside the BDR91with a Wago connector and closed the cover.

The app now can instruct the receiver to turn off heating and boost hot water, However, the app actions have no impact on the boiler's activity. It just keeps on heating.

I'll double check the wiring to the wireless receiver next.

Malcolm_J

@wateroakley Problem solved :-)

I carefully checked over the wiring to be sure I'd not connected anything wrongly. All OK at the wireless receiver. Traced back the wires from there to the rat's nest junction box and found that the one connected to CH NO was hanging with no connection! I then started at the BDR91 and worked out what it was connected to. Decided to remove the BDR91 altogether and connect the hanging CH NO wire to the wire that the B/CH NO wire was connected to, which led towards the boiler.

This all seemed to work better, and once I'd modified some schedules for the smart TRVs I could see the boiler cycling off when commanded by the app.

I also set up the hot water schedule as I wanted it (only needs 1hr each morning) and was puzzled as to why it didn't fire up as commanded - until I tweaked the tank mounted thermostat.

Woke up this morning to a tank full of hot water and a warm house. Happy chap.

Thanks again.

wateroakley

@Malcolm_J Pleased to hear that the problem is solved!