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Thread: 2 zone under floor heating thermostat

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    2 zone under floor heating thermostat

    Hi
    I went to customer who has under floor heating where the thermostats and double pole isolators were causing problems. 2 had burnt out one was busy in the process of melting (i can smell burning!). Did the usual checks, then temporarily connected the under floor heating load just to see the current draw. 18 amps at one stat point and and 21 amps going through another. That's either a lot of under floor heating or there is some other fault. At these 2 point there are 2 pairs of cables going down to the under floor heating (2.5mm flat coming in to supply it). I was wondering does anyone know anywhere where I can get a 2 zone thermostat. in other words one stat, with 2 switching points so the load can be switched by 2 contacts rather than the entire load going through one.

    Any ideas?

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    Diamond Member AndyD's Avatar
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    I think you're going to struggle to find any standard room thermostat that can switch 18 or 21 Amps directly. I just had a look through my Orbis and Honeywell catalogues and 15 or 16 Amps is the max contact switching capacity, the majority are actually 5, 8 or 10 Amp. You're probably going to need relays or small contactors but how much room have you got to play with? I've got a feeling the heaters are incorrectly installed, 18 and 21 Amps sounds way too high for a domestic underfloor heating in a single circuit.
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    Yep that's what i thought. Going to take the new Thermal imaging camera and see just how much of the floor is covered by underfloor heating. I estimate you would have to have 20 square meters to draw that much current. Some of the points where teh stats are have 2 cables going down floor. From there I don't know what happens yet. I haven't heard back from the customer so i'm guessing that someone provided him with some standard 16 amp stats and they should be melting anytime soon.

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by skatingsparks View Post
    ...... I haven't heard back from the customer...
    Maybe not hearing back from the customer would be the preferrable outcome with this particular job.
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