If its twin capillary, where is the second capillary pocket on the cylinder and what is the correct stat model and has that also got two capillarys and what is its switching differential and are you getting and installing one of them?
Boiler firing constantly for hot watere
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They both go into the same pocket, it seems one is for the stat and one for the thermal cut out.
The stat in it is the BTS60109, and cotherm have confirmed it is very sensitive and doesn’t have much/any differential. Their other models have 5/8 degrees as standard.
Does the overheat stat need to be quite sensitive? If so, would that mean the setpoint part of this combined stat also needs to be sensitive? I'm just trying to think of a reason for the small differential.
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The control (stat) part, 10C to 72C and the thermal cutout set at 82C are, in effect two stats wired in series so I cant' see any reason why the control stat part differential can't be 5C to 10C, and if required for tight control of the trip temperature at 82C then the thermal cut out part have a 1C differential, I don't really think though that this is necessary as once the thermal cutout operates at 82C then a 5C/10C reset differential shouldn't compromise its operation/purpose.
Cotherm should advise if they have a similar combined unit with a sensible differential.
My oil fired boiler has a overheat stat, I tested it 18 years ago when I installed the boiler and it certainly has ~ a 10C reset differential, the control stat has a similar differential.
Cotherm should advise if they have a similar combined unit with a sensible differential.
My oil fired boiler has a overheat stat, I tested it 18 years ago when I installed the boiler and it certainly has ~ a 10C reset differential, the control stat has a similar differential.
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I wonder whether other unvented cylinders also work like the OP's? The OP only seems to have found out through not having a timer. Most people would never know. Heatrae Sadia and Megaflo are big players, I believe. It would be strange for them to be so different to other brands.
Probaby not, Cotherm by email say, regarding the BTS6019, "Santon originally determined the spec of this thermostat, and it is supposed to have a tight tolerance to maintain the water temp." this stat is only used by Santon, they (Cotherm) said they could specify a different BTS stat with a 5C to 8C differential, so maybe Paul is looking at this.
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Thanks, yea they confirmed the same to me, so I am somewhat stuck as it stands, however with a timer on it I am definitely burning less gas!
I think the tank itself will likely need replaced in the next few years given the heat loss, so happy to wait it out now I know what the issue is, and will likely be back for some new tank recommendations!
Many thanks for everyone’s help and narrowing down the issue, really have learnt a lot!
Most heating coil (hot) inlet is high up on the cylinder and the (cold) return is near the bottom and the cylinder stat would normally be ~ a third the way up from the coil return, but the OPs (post #62) is very similar to this one with the coil flow/return at the bottom so not sure how high the coil extends upwards, the cold water inlet is almost directly adjacent to the stat so it would seem that any, even a very small HW demand will switch the stat to start reheating the cylinder.
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If the stat was higher you would have less hot water and most of the cylinder water would be cold.
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