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Installing a pipe stat in series with existing frost stat

Discussion in 'Plumbing and Central Heating' started by Attridgeous, 27 Jul 2015.

  1. Attridgeous

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    Hi everyone, I currently have my boiler installed in an outhouse attached to the kitchen which has no radiators and can get very cold in winter. There is already a frost stat installed, with the obvious problem that when the temp falls below 3 degrees the frost stat kicks in but doesn't then go off as the air temp in the room never rises. I would therefore like to install a pipe stat in series with the frost stat so that when the return pipe temp reaches a set level (say 20c), it stops the frost stat from calling for further heat.

    I would like to run my plans by you guys so you can let me know if the following is correct...

    I plan to buy a low limit pipe stat. My current frost stat is wired up to the mains (it's a T4360A with mains connected to terminal 1) and terminal 3 is connected directly to the call for heat terminal on my boiler (a Baxi 105 e with terminal box connections L, N, E, 1 and 2; 2 being the call for heat terminal).

    As a side note, I was surprised there was only 1 connection from my frost stat to my boiler, but I assume this is fine as mains power is supplied from elsewhere. Is this correct?

    My plan would be to simply disconnect the frost stat from boiler terminal 2 and connect it instead to terminal 1 on the pipe stat (an L641B1004). Terminal C on the pipe stat would then connect up to terminal 2 on the boiler where the frost stat was originally connected. Based on this, there should be no call for heat when the temp is above the safe temp as terminal C on the pipe stat will be connected to terminal 2 on the pipe stat in this instance. But, when the temp falls below the safe level terminal C switches to terminal 1 on the pipe stat and you have your circuit (assuming the frost stat has detected a below limit temp too).

    Does this all sound correct? Am I right in thinking that with this setup there will only ever be a power supply to the pipe stat when the frost stat detects a temperature below its set limit?

    Many thanks guys.
     
  2. Attridgeous

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    As a follow up my plan is based on this circuit diagram, incorporating the frost stat and the pipe stat in series.
     

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  3. Phill Peck

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    yes that looks right
    I'd fit pipe stat to return and ensure bypass is adequately open.

    Doesn't matter. Which stat is first in series. They work in series
     
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