Just thought I should give readers an explanation on why the Domestic Hot Water [DHW] BDR91 relay might appear not to be working if you have several timed calls for hot water.
My system was originally set so that Hot Water was timed to come on at 7.30 a.m. and again at 5.30 p.m. for an hour or so.
About two weeks ago, I then added a third time slot for DHW around 12.30 p.m. but I soon noticed that the lunchtime call for DHW didn't always seem to show an increase in water temperature.
I thought the CS92 sensor was not responding as the controller did not appear to be turning on the Hot Water BDR91. I checked the wireless signal quality to the CS92, which was fine showing five red LED flashes. I kept turning on the request for hot water via the Evohome app or controller but the BDR91 green LED would not turn on.
After hours playing around with the controller/app/BDR91/CS92, I have found the problem.
There is a parameter setting on the controller's installer settings for Hot Water labelled "Hot Water Differential". This is defaulted to 10⁰C.
What this does is prevent the controller turning on the DHW BDR91 if the temperature reported by the CS92 sensor is within the differential of 10⁰C of the maximum setting, which is by default 60⁰C. So if water temperature is say 55⁰ in the cylinder, this is only 5⁰C from maximum required of 60⁰C, so no switch on command is sent.
The solution is to change this Hot Water Differential to say 5⁰C if you want more than one morning and evening timed call for hot water. The temperature drop will naturally occur overnight and between morning and evening but not usually between morning and lunchtime. If you always want water turned on, you could even drop the differential to 0⁰C
My system was originally set so that Hot Water was timed to come on at 7.30 a.m. and again at 5.30 p.m. for an hour or so.
About two weeks ago, I then added a third time slot for DHW around 12.30 p.m. but I soon noticed that the lunchtime call for DHW didn't always seem to show an increase in water temperature.
I thought the CS92 sensor was not responding as the controller did not appear to be turning on the Hot Water BDR91. I checked the wireless signal quality to the CS92, which was fine showing five red LED flashes. I kept turning on the request for hot water via the Evohome app or controller but the BDR91 green LED would not turn on.
After hours playing around with the controller/app/BDR91/CS92, I have found the problem.
There is a parameter setting on the controller's installer settings for Hot Water labelled "Hot Water Differential". This is defaulted to 10⁰C.
What this does is prevent the controller turning on the DHW BDR91 if the temperature reported by the CS92 sensor is within the differential of 10⁰C of the maximum setting, which is by default 60⁰C. So if water temperature is say 55⁰ in the cylinder, this is only 5⁰C from maximum required of 60⁰C, so no switch on command is sent.
The solution is to change this Hot Water Differential to say 5⁰C if you want more than one morning and evening timed call for hot water. The temperature drop will naturally occur overnight and between morning and evening but not usually between morning and lunchtime. If you always want water turned on, you could even drop the differential to 0⁰C
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