Controlling a radiator zone with underfloor heating

Discussion in 'Plumbing and Central Heating' started by andymach23, 29 Jan 2010.

  1. andymach23

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    Hi Everyone

    First post on this forum :D. There seems to be some very knowledgable posters, so here goes.....

    I have recently had a new heating system installed, and have just got a 2 channel programmer fitted, as I was advised I needed this to give me full control of my system. It's wet underfloor downstairs and radiators upstairs. There is a 2-way motorised valve for the radiators. The boiler is a gas combi.

    The UFH (under floor) side of the system is controlled by the hot water side of the programmer. This seems to work ok. When the UFH thermostats are satisfied for heat the boiler is basically off, ie no burner light is on and the central heating light off. When a thermostat requres heat the boiler fires up as expected.

    The central heating side of the programmer controls the radiators. I have a room thermostat upstairs. If the radiators are time programmed to be off, and the room thermostat is set higher than the current room temp, the boiler will run with the central heating light on and the burner will run periodically.

    It seems that the room thermostat is over-riding the time on the programmer. It is making the boiler fire even though the programmer says the radiators should be off. The radiators don't come on however, as the motorised valve stays closed. It looks like the central heating side of the programmer is controlling the motorised valve only and not the boiler function.
    As I only need a couple of hours of radiator heat upstairs during the day it seems very wasteful that the boiler should keep running based on the upstairs room stat reading.

    Does this sound normal? I would of thought that the programmer should switch the boiler off period, and the upstairs room stat should only come into play during the radiators programmed 'on time.'

    Can anyone sort this one out for me? Sorry this is a bit long winded :confused:

    Cheers, Andy
     
  2. collyplumb

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    Hi Andy

    Its sounds like the room stat has been wired directly into the boiler as apposed to across the switched live. Does the central heating go off if the room stat is satisfied but the timer remains on. What type of boiler do you have?
     
  3. andymach23

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    Hi, thanks for the reply

    I have a Baxi Duo Tech Combi. I am not totally sure if the heating goes off if the room stat is satisfied. I will check this later and post back when I get home.

    For further info, I have a Myson wireless control centre. Channels 1-5 are for the UFH thermostats. Channel 6 seems to be used for the room thermo upstairs. 7 & 8 looks like being for the boiler/pump.

    Cheers, Andy
     
  4. andymach23

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    Hi again.

    I just did some more testing.

    If the the CH (radiators) timer is on and the upstairs radiator room stat is satisfied the boiler goes off.

    If the CH timer goes off and the upstairs thermostat is not satisfied the boiler keeps going, but the valve for the radiators is closed.

    If the CH timer is on and the UFH timer is switched off, the wiring centre closes down completely with no power and the boiler switches off. The UFH timer over rides everything. To get the boiler to fire again I had to use it's reset function.

    The UFH is wired to the hot water side of the programmer but I suppose the programmer doesn't differentiate between running hot water and UFH.

    Just to clarify, my expectation for this system is....

    1. That I shoud be able to have the UFH off and just run the radiators only, and vice versa. Therefore they are behaving as completely separate systems with their own "on and off" cycles.

    2. The UFH and CH should only run the boiler when their timer is on and their thermostats are requesting heat.

    3. The UFH and CH should be able to turn the boiler off and on independently via their thermostats.

    Is this correct?

    Cheers, Andy
     
  5. Terrywookfit

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    You need a zone valve for each zone to control independantly.
     
  6. collyplumb

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    Your expectations are correct. The boiler should be fed by a permanent live, neutral and earth from a fused spur. (if no heat is called for the boiler should still be on, not firing but on)
    A live, neutral and earth to the wiring center must also be taken from the spur.
    The wiring could have gone wrong at a number of points as with these boilers it requires a link to be taken from the boiler (from the terminal 1 and 2) then from terminal 2 the switch live must be fed to the timer com then from hot water on (for underfloor heating) to UHF 2-port valve (grey) then orange back to boiler terminal 1. That will create the switched live link for the underfloor heating. For the radiators.. you already have the wire going to com so take one from CH on to roomstat then from roomstat to grey of CH 2-port and then orange from 2 port back to boiler terminal 1.

    I hope this helps. The boiler manual should be able to help you out as well
     
  7. andymach23

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    Much obliged Collyplumb. Great info there. I have down loaded the Baxi manual so will check it out.

    Do you think I need another zone valve as Terrywookfit says, to get this to work properly or is the one valve enough for all of this? :D


    Cheers, Andy
     
  8. collyplumb

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    Yes, a little late from me. 2 zone valves a must. Have a look at the requirements for an auto bypass valve for the pump overrun.
     
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  9. andymach23

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    Thanks collyplumb

    I'm going to arrange for the boiler/CH installer to come round and check out whats required. There's no point tacking the wiring until the correct hardware is in place.

    Appreciate the quality advice :D

    Cheers, Andy
     

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