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Inherited system another anomaly!

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Bogart

Bogart

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The more I investigate the system I have inherited I wonder who was employed to maintain it?
A couple of meters along the boiler output point is a pipe stat. A Honeywell L641B1004 which has a range of 10 to 40˚C, . I think what should have been installed is a L641B1012 which has a range of 50 to 95˚C. There is a frost stat nearby so assuming not meant to be another frost stat
 
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What does the boiler supply/ heat ?
 
Is there any tees before the stat ?
 
Nothing at all leaves the boiler in 28mm stat is positioned about 75mm after a 90deg elbow which as mentioned before is about 2m from the boiler outlet.
 
Do you know if the stat is controlling the pump ?
 
Sounds like the correct pipe stat as it needs to be set at 25 C. Only thing is it should be on the return and within 600mm of boiler
 
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Checked and found both are operating as frost stats. If either are switched on the boiler comes on but not the pump! All seems a bit odd as the two stats are literally a foot apart. So much for my theory that the pipe stat was an overtemp device.
 
Bogart said:
Checked and found both are operating as frost stats. If either are switched on the boiler comes on but not the pump! All seems a bit odd as the two stats are literally a foot apart. So much for my theory that the pipe stat was an overtemp device.
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The frost stat (which measures air temperature) and pipe stat (measures water temp and fitted to return pipe) should be wired in series. The boiler lights when the air temperature drops below the frost stat setting (5-10C). The pipe stat turns the boiler off when the water returning to the boiler reaches the set temperature (25C).

If there is no pipe stat, the boiler temperature will rise until the boiler stat operates - may be 80C. This would heat the house unnecessarily and be wasteful.
 
Well I reckon the pipe stat is stuffed as it does nothing. If I turn on the boiler by raising the frost stat up, so the boiler kicks in, the pipe stat can be set anywhere between the minimum 10˚C and the max 40˚C with no result. By my reckoning from what "doitmyself" said the stat must be shorted, or boiler would not fire. Finally is not 25˚C rather high, why heat the whole setup to this figure as a frost protection? Anyway my setup does not switch on the pump so seems to defeating itself!
 
Here is a wiring diagram showing how the frost and pipe stats should be connected. Use it to check your wiring. (Ignore terminal numbers - assumes Honeywell method - valve wire colours are the thing to follow.)

Don't forget that 25C is the temperature of the water in the pipe, not the air temperature. When the boiler is running for heating the water could be as much as 80C.

The frost/pipe stats should turn the pump on so the water circulates.

Could it be a DIY installation of the pipe/frost stat?

Frost Kit.jpg
 
Hi
Sounds very much like a DIY job, and a poor one at that. Having delved in found pipe stat wire in the terminal but covered in insulation tape, do not ask why, I have no idea either. System now seems to be working ok and pump now does run. Have copied your diagram for future reference. I never knew about the stat switching the boiler off, one learns something new everyday, many thanks.
 
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