With the cold weather coming along I found out my mother was controlling the house central heating by turning the heating flow control up and down. I asked why she did not use the Honeywell cm927 program controller paired up with a BDR 91 receiver? I put the controller into manual called up a temperature about a couple of degrees above the indicated temp and the BDR green light lit up but the boiler flame light did not come on the display for 4-5 mins, there seems to be this lag or the controller is calling for heat and the boiler does not respond. I revealed this wiring in the boiler there are 2 wires going to the outdoor temp compensator and the BDR power wires are connected to the mains terminals of the boiler, I'm nor sure if this is another way of connecting it, it looks nothing like the examples I have seen on the Worcester Bosch You Tube video about fitting third party controls. Can anyone please help, cannot contact the original plumber. Have included photos of wiring in BDR and boiler. Can anyone please advise?
Is the BDR 91 wired up correctly to Worcester Greenstar 30i Combi Boiler Correctly?
- Thread starter Paulmuzza
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Not clear what exactly those grey and black wires are connected to in the boiler, but it's wired incorrectly. As it is, the boiler will be on continuously, and has been wasting vast amounts of gas for however long it's been like that.
To fix:
White link between L and CH is removed
black wire to L
grey wire to CH.
To fix:
White link between L and CH is removed
black wire to L
grey wire to CH.
Could be 24v side by the looks of it, in which case only 230v links need be removed, as I’m sure you know
As the OP says...
It would be interesting to know how the on/off receiver may be (at least partially) triggering the boiler from those terminals?
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Interesting as to how central heating should be controlled. I remember with my late mothers the thermostat lost RF link and failed to turn off, and the room overheated, this should not have happened, as even without the wall thermostat the TRV should have stopped the room over heating.
I am not saying an outside thermostat is the way to go, but I am saying control specially with a modulating boiler is not as simple as fitting a single wall thermostat, it may work with an open plan home, but most home have things called doors.
So basic control with a home with doors to each room, is hot water is pumped from the boiler to a series of radiators, each with a TRV plus a by-pass valve, as each room reaches the temperature set, the TRV's start to close, and the water first is diverted to those radiators in rooms not yet warm enough and then through the by-pass valve, this means the return water slowly gets hotter and hotter, and the boiler senses this and slowly turns down the output further and further until it can't go any lower, then it starts switching off and on, know as a mark/space ratio, however what it can't do is switch fully off, as once the water stops flowing it can't know if the TRV's are open or closed, so it needs some thing to tell it in summer to turn off.
In most situations we don't want heating 24/7, or at least want rooms cooler overnight, so we want some internal programmable device that can turn heating as a whole on and off, but there would be nothing wrong with simply having a thermostat outside to turn heating off on warm days.
However likely due to radiant heat, in summer an air temperature of 17ºC is nice, but that feels cold in winter. And also in the summer last thing one wants to do is heat the home in the morning then have to cool it in the afternoon, so ones aim is to keep home cool.
Also air flow within the room, my living room has three TRV's in it, two on radiators, and a broken one on the fire place which still records the temperature, all electronic so I can say at moment the three show 14.2ºC, 16ºC and 21ºC the latter is the broken one on the fire place, but it shows even within the same room how much the temperature can vary. What we hope is the device monitoring the room temperature to control it, is in the natural air flow, diagrams like this
show expected air flow, so to measure the return air would seem to make sense, so the location of the TRV bottom of radiators slightly off to one side does seem a near ideal location to measure temperature of whole room, the broken TRV on the fire place is really too high and too close to centre of the home.
I do have some things to move the air, two kittens running around the room, but clearly not enough, but each book one reads has a different diagram
and one has to question do any relate to my home? My thermostat to turn whole boiler on/off is in the hall about centre of the house and in a room where thermals are unlikely to work due to it having stairs in it to upper floor, so wall thermostat shows 17ºC and the TRV shows 14ºC not by any stretch ideal as the wall thermostat turns off heating to whole upper house, the flat under house has its own wall thermostat.
So the heating and ventilation engineer should design the heating to suit the house, but what happens is a plumber puts in a system the same as many other homes and leaves to owner to sort it out latter, this is clear as we find bedrooms used as offices, home work rooms, craft rooms etc. But the heating system requires all or non of bedrooms heated with the use a zone valves, when electronic TRV's are likely cheaper and do each room independently.
As the song says little boxes and they all turn out the same, but in real life that is not true. If there was a instruction set which said this is how we have designed the central heating to work, we could look at it and say, it does or doesn't work as designed, but no one seems to do that, so we have to assume.
I would assume your boiler is wired wrong, but if the TRV's and lock shield valves are set correctly it should not matter, it should still work.
I am not saying an outside thermostat is the way to go, but I am saying control specially with a modulating boiler is not as simple as fitting a single wall thermostat, it may work with an open plan home, but most home have things called doors.
So basic control with a home with doors to each room, is hot water is pumped from the boiler to a series of radiators, each with a TRV plus a by-pass valve, as each room reaches the temperature set, the TRV's start to close, and the water first is diverted to those radiators in rooms not yet warm enough and then through the by-pass valve, this means the return water slowly gets hotter and hotter, and the boiler senses this and slowly turns down the output further and further until it can't go any lower, then it starts switching off and on, know as a mark/space ratio, however what it can't do is switch fully off, as once the water stops flowing it can't know if the TRV's are open or closed, so it needs some thing to tell it in summer to turn off.
In most situations we don't want heating 24/7, or at least want rooms cooler overnight, so we want some internal programmable device that can turn heating as a whole on and off, but there would be nothing wrong with simply having a thermostat outside to turn heating off on warm days.
However likely due to radiant heat, in summer an air temperature of 17ºC is nice, but that feels cold in winter. And also in the summer last thing one wants to do is heat the home in the morning then have to cool it in the afternoon, so ones aim is to keep home cool.
Also air flow within the room, my living room has three TRV's in it, two on radiators, and a broken one on the fire place which still records the temperature, all electronic so I can say at moment the three show 14.2ºC, 16ºC and 21ºC the latter is the broken one on the fire place, but it shows even within the same room how much the temperature can vary. What we hope is the device monitoring the room temperature to control it, is in the natural air flow, diagrams like this
show expected air flow, so to measure the return air would seem to make sense, so the location of the TRV bottom of radiators slightly off to one side does seem a near ideal location to measure temperature of whole room, the broken TRV on the fire place is really too high and too close to centre of the home.I do have some things to move the air, two kittens running around the room, but clearly not enough, but each book one reads has a different diagram
and one has to question do any relate to my home? My thermostat to turn whole boiler on/off is in the hall about centre of the house and in a room where thermals are unlikely to work due to it having stairs in it to upper floor, so wall thermostat shows 17ºC and the TRV shows 14ºC not by any stretch ideal as the wall thermostat turns off heating to whole upper house, the flat under house has its own wall thermostat.So the heating and ventilation engineer should design the heating to suit the house, but what happens is a plumber puts in a system the same as many other homes and leaves to owner to sort it out latter, this is clear as we find bedrooms used as offices, home work rooms, craft rooms etc. But the heating system requires all or non of bedrooms heated with the use a zone valves, when electronic TRV's are likely cheaper and do each room independently.
As the song says little boxes and they all turn out the same, but in real life that is not true. If there was a instruction set which said this is how we have designed the central heating to work, we could look at it and say, it does or doesn't work as designed, but no one seems to do that, so we have to assume.
I would assume your boiler is wired wrong, but if the TRV's and lock shield valves are set correctly it should not matter, it should still work.
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