Wet ufh system and radiators off same combi boiler

Discussion in 'Plumbing and Central Heating' started by Bob Wilson, 7 Dec 2021.

  1. Bob Wilson

    Bob Wilson

    Joined:
    7 Dec 2021
    Messages:
    1
    Thanks Received:
    0
    Country:
    United Kingdom
    We have just had an extention built with wet under floor heating in screed, but still have radiators in the old part of the house. The system has a zone valve that controls the radiators and the wiring harness seems to mean it doesnt need a second zone valve for the ufh part. Both the radiators and underfloor use a common boiler return.

    The problem is this - if I use the underfloor heating at a high temp (45c) the radiators heat up even when the thermostat on that zone valve is closed. What seems to be happening is that the outlet from the ufh manifold is backing up into the radiators via the common return. Has the plumber forgot to fit a non return valve or something?

    I can minimise the problem by using the lowest temperature on the manifold mixer valve because then the return is 24c and hardly noticeable, but I would like to run the ufh at 45c to heat the room quicker.
     
  2. DP

    DP

    Joined:
    10 Dec 2003
    Messages:
    15,188
    Thanks Received:
    3,375
    Location:
    Glasgow
    Country:
    United Kingdom
    Replumb so that returns are commoned at the boiler
     
  3. Sponsored Links
  4. BlueLoo

    BlueLoo

    Joined:
    1 Dec 2021
    Messages:
    1,056
    Thanks Received:
    141
    Country:
    Ireland
    Forgive me if i have this wrong, there is only one zone valve?

    Each zone should have its own valve i would think.

    UFH-zone valve.
    House-zone valve.

    Common return is ok, but the feed needs to be valved.

    Would be my opinion.
     
  5. Mr Chibs

    Mr Chibs

    Joined:
    28 Jul 2015
    Messages:
    1,098
    Thanks Received:
    182
    Country:
    United Kingdom
    I have similar set-up and have two zone valves, one for house rads, the other for ufh in one room. Both can be controlled independently.

    Can’t you turn the boiler up slightly And used the ufh blending valve to reduce water temperature?

    FWIW, Just looked at my boiler rad temp 47°
     
  6. Sponsored Links
  7. Madrab

    Madrab

    Joined:
    4 Oct 2012
    Messages:
    8,568
    Thanks Received:
    2,482
    Location:
    East Renfrewshire
    Country:
    United Kingdom
    You should have a 2 port valve on the UFH prior to the UFH pump, that is controlled by the UFH thermostat that should be in the extension?? Depending on where they have plumbed the return from the UFH into the main return for the CH, then it sounds like you may be getting reverse circulation.

    Bit of a no brainer ... get them back in to fix it, it's their responsibility!!
     
    • Like Like x 1
Loading...

Share This Page