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Honeywell Low & Hi limit pipe stats

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eaglesalz

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Joined: 16 May 2011
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Location: Sussex,
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PostPosted: Mon May 16, 2011 10:20 am Reply with quote

Hello, Can anyone tell me how to wire in Honeywell L641 low limit and a Honeywell L641 hi limit pipe stat. This is for a solid fuel (wood) stove so want to switch off the pump when fire dies down and then switches on when fire is lit and water is heated. Thanks Jeff
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Agile

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PostPosted: Mon May 16, 2011 11:22 am Reply with quote

Where in the circuit has the pump been fitted?
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eaglesalz

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PostPosted: Mon May 16, 2011 12:43 pm Reply with quote

Hello the pump is wired into the wiring centre where a cylinder stat and room stat is wired in, not that these are any good as they can't shut the boiler down when their temp has been reached but I wired them in anyway. Do I just wire the pump through the contacts on the pipe stats, but I can't seem to get my head around the low & the high. Am I right in thinking the low needs to go on the return and the high needs to go on the flow, and how do the 2 stats work together. Also has the control for switching on and off, again no good unless something gets out and puts wood in the boiler and lights it, but it tells the time. The programmer is a Honeywell ST6400C 1003, Cylinder stat L641A 1039, Room stat honeywell T6360B & Honeywell HJB10 wiring centre and the 2 hi & low pipe stats. Pump Live is wired to Orange on the mid position valve and term 1 on the cylinder stat.
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commercialman

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PostPosted: Mon May 16, 2011 5:54 pm Reply with quote

Can't see the reason for the low limit stat , for what you intend doing just use the high limit stat & switch circulator via terminal 2 (NO when call for heat).


Last edited by commercialman on Mon May 16, 2011 6:02 pm, edited 1 time in total
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dcds4

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PostPosted: Mon May 16, 2011 6:00 pm Reply with quote

as said lose the low limit stat, unless you are on gravity hw then it wont work very well
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sweet

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PostPosted: Mon May 16, 2011 10:53 pm Reply with quote

I wouldn't entertain these people...
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croydoncorgi

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PostPosted: Tue May 17, 2011 12:52 am Reply with quote

If the system DEPENDS on the pump to take the heat away when the fire is burning, you MUST NOT change it so that the pump 'might not' run. There might be an overheat and explosion risk...

On the other hand, if the system is properly designed to cope with overheating by other means (not depending on the pump), then fitting a Low Limit arrangement to stop the pump ciculating cold water makes sense. Pipestats usually have three terminals (Common, Make on Rise, Break on Rise). Why is wiring a problem?

(In fact, if the system depends on the pump for safe operation, it's already dangerous! What happens during a power failure? If the pump jams/burns out? Putting on more fallible components makes it worse!)
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bengasman

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PostPosted: Tue May 17, 2011 7:06 am Reply with quote

Solid fuel systems are really not suitable for diy jobs like this.
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eaglesalz

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PostPosted: Tue May 17, 2011 7:47 am Reply with quote

Hello Thanks for the replys. @ croydon the system has a heat sink (rad) which is befor the pump and mid valve and a auto bypass fitted so if power fail then gravity does the rest and no risk of explosion and is also open vented. the low limit is for when the water being heated falls to 40c or less, I dont want cold water being pumped around the system and taking all the heat back out of the hot water storage. As I see it are the 2 stats required, as if there is only the hi limit then the pump will not switch off when the fire dies down.
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eaglesalz

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PostPosted: Tue May 17, 2011 7:52 am Reply with quote

The pump is fitted after the cold feed and vent pipe and the heat sink rad, so if the pump fails the hot water has somewhere to to dissipate the heat. there is also a auto bypass fitted.
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commercialman

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PostPosted: Tue May 17, 2011 4:43 pm Reply with quote

eaglesalz wrote:
As I see it are the 2 stats required, as if there is only the hi limit then the pump will not switch off when the fire dies down.


As i said , only one stat required , switching the pump via terminal 2 on pipe stat will bring the pump on @ temps ABOVE stat setting , when temp falls below stat setting pump will switch OFF...............example , set stat to 60 degrees & pump will run above this temp , fire dies down & pump will switch off.
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eaglesalz (17 May 2011)
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eaglesalz

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PostPosted: Tue May 17, 2011 6:00 pm Reply with quote

Thanks for that commercialman, makes sense now you explained it to me, so I just wire to live on pump through the thermostat terminals as I see it.
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Norcon

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PostPosted: Tue May 17, 2011 6:14 pm Reply with quote

commercialman wrote:
Can't see the reason for the low limit stat , for what you intend doing just use the high limit stat & switch circulator via terminal 2 (NO when call for heat).


There's a number of reasons for a low limit stat and it should not be omitted.
Woodwarm explain it very well in their MI's. Page 17....

http://tinyurl.com/6xcte8y

The OP should adhere to the MI's (or use the services of someone who will) and most will recommend a lo limit stat in conjunction with a high limit stat.
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commercialman

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PostPosted: Tue May 17, 2011 7:53 pm Reply with quote

[quote="Norcon";p="1991459"]
There's a number of reasons for a low limit stat and it should not be omitted.
Woodwarm explain it very well in their MI's. Page 17....
quote]

Woodwarm mention the installation of high & low pipe stats , some other manufactures don't , obviously adhere to the MIs in any event...............switching pump via high limit stat alone AS ADVISED will not contribute to back end corrosion (condensation).
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Norcon

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PostPosted: Tue May 17, 2011 10:40 pm Reply with quote

Quote:
switching pump via high limit stat alone AS ADVISED will not contribute to back end corrosion (condensation).


Can you guarantee that?
You'll certainly be running the firebox much cooler with the possibility of removing heat from a hot water cylinder( creating other problems) and dumping it in the central heating especially if an injector T is fitted.

Not enough info to advise here anyway. What type of stove,two, three or four pipe layout, is a hot cylinder connected?, heat sink dissipation allowance ???? etc etc....
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