Red hot radiators despite thermostatic valves set on 1

Discussion in 'Plumbers' Talk' started by Collier1718, Jan 12, 2013.

  1. Collier1718

    Collier1718 New Member

    We recently removed a radiator from our central heating combi boiler system. We did it in the way you remove one when you decorate but just didn't put t back. When we refilled the system the radiators wouldn't heat up for hours until we turned the boiler off and then back on after bleeding all the radiators. Our upstairs radiators have thermostatic radiator valves on them which worked perfectly until now. They are red hot on all settings except off when
     
  2. Collier1718

    Collier1718 New Member

    they do actually turn off.
    Any suggestions as to what to do would be greatly appreciated.
     
  3. teabreak

    teabreak Well-Known Member

    Thermostatic valves do not control the temperature of radiators they simply turn them on or off according to the room temperature.  The actual surface temprature of the rad is decided by the boiler thermostat, perhaps when turning the boiler off and back on you may have set the boiler thermostat at a higher temperature.


    Regards,
    teabreak
     
  4. petertheplumber

    petertheplumber New Member

    If you drained the system to remove the rad make sure all rads are bled of air and then make sure boiler pressure is 3/4-1 bar.
     
  5. Collier, as teabreak says, just turning the TRV down to, say, 1 will not turn the rad temp down - if the room is cold. The numbers on the TRV correspond to room temperatures (3 is roughly around 20oC , I think), so the TRV - and the rad - won't turn off until the room is at that temp. They sound as tho' they're working fine - they shut off completely when you turn them to 'off' - and it would be very unusual for all the upstairs TRVs to have failed at the same time.

    Don;t forget, it's a bit cold at the mo', so it could be that the TRVs are simply trying to keep the rads on for longer compared to when you last used the CH, pre-decorating.

    Do you have two rooms upstairs that are similar sizes and temp (windows facing the same way)? If so, turn on your heating and turn on one TRV to '3' and t'other to '1'. Leave it for a half hour or so, and then check both radiator temps to the touch. I bets the one one (ie: the '1' one...) is much cooler because that room will have reachewd the temp which corresponds to the '1' and the TRV will have started to shut offski.
     
  6. Captain Leaky

    Captain Leaky New Member

    I have said it before and I'll say it again......the general public do not have a clue how TRV's work.... If I had a £1 for everytime I have to explain it to them I would be a very wealthy man.

    Oh wait.... I am apparently.!

    Keep asking ;)
     
  7. Ok then, smartass, how do they work?

    I mean, how does a small tube of melting wax push a plunger down against a powerful spring? And then allow it to retract agian as it cools?





    (I ask 'cos I ain't got a foffing clue... :()
     
  8. Collier1718

    Collier1718 New Member

    Thanks for all the replies.

    Tea break - will check the temp - don't think we changed it but you never know!
    Yes Captain Leaky - I know nothing ;) .
    Devils A - will give it a try as we do have 2 similar rooms facing the same direction.
     
  9. sam spade

    sam spade Active Member

    It not a case of the wax melting, but of it expanding and contracting

    Most TRVs now use a liquid filled sensor, which expands when it is heated and contracts when it cools.

    See http://heating.danfoss.co.uk/PCMPDF/operation_princip_facelift.swf
     
  10. Cheers Sam. AaaAAAaaaaahhh! (Good diagram :))

    Impressive to think how much the liquid expands over such a small temp range.
     
  11. Glad its Friday

    Glad its Friday Active Member

    Are your TRV heads properly attached to the body of the valve?

    Turn the TRV to the maximum setting (no 5 or 6 etc)
    Then tighten down the TRV to the body of the TRV (this is usually via a knurled chrome ring although different makes have different systems).
    Finally pinch up with a pair of pump pliers or similar.
     

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