The Efficient Home Forum

Hi everyone,

I had a Atag Q38S installed in 2015 and it was controlled by the Atag BrainQ. It was a replacement for an old fuel boiler. At the time the house was rented and the tenants were doing the following: week days from 6.00 pm - 22°C until 8:00 am the next morning and back to 16°C during the day. On weekends Friday 6:00 pm - 22°C until Monday 8:00 am. So basically 22°C when they were home, including during the night. They never reported any issue. When I came to fix or do some maintenance work, I didn't notice any issue.

When I moved back in the house in 2018, the first thing I did was to program the heater more efficiently: 20°C when at home, 16°C during the night, when away...

This efficiency made it obvious that the house was not well balanced (heating wise):

• - The main room with the thermostat was at temperature much faster than the rest of the house
  - The sun input is bigger in the main room than the rest of the house
  - The exposure is lower in the main room than the rest of the house

What I did:

• - I tried to reduce the flow to the main room, but there wasn't any modulation other than the thermostatic bulb.
  - I insulated the the attic floor in hopes it would maintain the temperature longer (and lower the heating bill).

Result:

• - Mold in the bathroom, despite the extractor (150mm).
  - Having to use an electric heater in the bathroom which was at 16-18°C despite the winters being mild.
  - Impossible the use a spare bedroom as an office, unless knowing the night before you were going to use it or heating it all the time.
  - Some of the rooms dropping below 10°C while we were away but the main room still at 16°C

After the last winter I decided to switch to an Evohome system and use the boiler's OpenTherm capabilities. I waited until the maintenance was scheduled to talk with the Atag technician.
Only 2 things to do:

• - Plug the R8810A118 in the slots 20 and 21 of the boiler, after unplugging the BrainQ.
  - Change parameter 60 to 2.

It didn't work, the light was on, the evohome was bound and all the HR92 were at maximum signal. No heating, no hot water. So after a few hours looking online and a cold shower the next day, I plugged back the BrainQ.
I sent an e-mail to Atag and waited. Luckily I had another maintenance planned elsewhere and the technician mentioned the e-mail. Apparently one more parameter has to be changed but it's protected, so he offered to come and change it the same day.

Well since then it's been working, only one HR92 is having trouble with the signal but every time I do a signal check for the zone, it's a 5 out 5 signal for every controller. I did reset the controllers and deleted the zone, but it already sent a default message once. I don't have any idea which one is at fault since the issue is gone by the time I catch it, only the error message is left on the Evohome's screen.
Otherwise the system capabilities are exactly what we needed, I'll check the meters to check on the consumption and if it's stay more or less the same that would be perfect.

I have a ATAG CBS150 (a hot water accumulator tank) which is monitored by the boiler, but since the BrainQ is unplugged I don't have any control over the DWH. I have no idea what the program is, only thing I can check is the temperature in the INFO menu.
If I understand correctly, I only have to place the Evohome Hot Water Kit sensor on the tank (through the insulation) and bind it to the Evohome, but I still have to bind a BDR91 that will control the 3 way valve. It's not a problem to leave the original sensor connected to the heater ?

Can someone give an insight to what the connections should be ?
If I'm not mistaken it should be 12-13-14 but I have no idea what I should connect...


Thanks for reading.

Sorry I can't help, but Atag don't supply via merchants so integrations and information isn't easy to come by.