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Discuss UFH won't go above 19 deg in the Underfloor Heating Forum area at UKPlumbersForums.co.uk.

  1. stig125

    stig125 New Member

    Hi all,
    I have wet UFH 4 Zones. I used to have HIVE controlling it but I wanted a better way of controlling Zones as I was wasting money having all 4 zones at the same temp.

    I have since dumped HIVE and have had emmeti actuators, Wiring centre and RF thermostats fitted.

    My problem is that it seems to struggle to reach 20 deg. In the lounge, for example, I have it set to come on at 7am with a target of 20deg. When I come downstairs it is at 19deg at 7am and calling for heat.By 9.15 it's still at 19 deg and still calling for heat. The boiler is coming on to it's request, albeit a bit delayed.
    By the time I left it had actually fallen to 18 deg but the floor seemed as warm as it was and it was still calling for heat.
    A check on the gas meter proved it had been using gas 2m3 over 2 hours and took the temp from 19 to 18 degrees for it..

    The house was completed in March this year and achieved and EPC rating of A, so I am not putting it down to heat loss at this point.

    My Mixer is set at 45deg and all flows react to the actuators as they should, so everything seems to be working. The manifold pump has 9 settings and is running at 4. It was set at 5 but I read that UFH needed a lower pump flow.

    Anyone got any ideas before my money is all spent on Blankets and British Gas
    Thanks

    Wal
     
    • Like Like x 1
  2. Last Plumber

    Last Plumber Plumber GSR Top Contributor!!

    You know that UFH is not the same as Radiators don't you?
    By that I mean, you can't expect it to come on at 7 am and warm the room like radiators would do !
    It will need to be on a lot longer or in many cases left on and set to 'maintain' a temperature !

    Just checking you are on the same page.
     
    • Like Like x 1
  3. chris watkins

    chris watkins Plumber

    So long as it has been designed correctly then the flow temperature will need to be increased to increase the floor surface temperature so that there is a greater differential to the air temp.

    However there are lots of variables to this like floor coverings, heat up times, heat losses etc
    As all the rooms are doing the same thing it i.e. not achieving the design room temperatures it is either the the floor surface temp is not hot enough or the length of time you have the system on for is not allowing the room air temp to reach those required.

    People who have U/F installed often think it can be used like a their old rad based systems i.e. stick it on an hour before you want it.
    U/F heated rooms can take a good couple of hours to reach the set temperature if it is cold both inside and out. Most will only raise room by 2deg C per hour.
     
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  4. stig125

    stig125 New Member

    Hiya, many thanks for your reply.
    I did know that UHF reacts differently to rads and was prepared for that, but when I had HIVE controlling all zones as one, if I put it to boost for 2 hours, it would be very slow at first then reach it's 2 hour mark and stop the boost. The temp would continue to rise from that point on as I guess the floor (tiled only throughout) would continue to emit heat into the room for a few hours.

    It was when I stopped HIVE and went to controllable zones that it started acting differently. I thought that by being able to lower the requirements of 1 or 2 rooms would increase the heat in the other 2 rooms. I think I may have got that wrong.. lol as I am probably still thinking in terms of rads instead of maintaining a temp.

    Sometimes, when you change what you have, you expect an instant result and when it acts differently to what you have thought.. you put it down to the change.

    Thanks again
    WaL
     
  5. stig125

    stig125 New Member

    Hiya chris, thanks for your reply.
    I was told not to run the flow temp at any higher than 45 deg and that 50 + deg could affect the screed or lift the tiles. I did think it may be the temp on the mixing pump but was worried to put it higher. You are so right when you say there are so many variables.. and the trouble is you look to the last thing changed and blame that..lol.

    What was bothering me was the fact that in 2 and a half hours it had managed to take temp in that zone from 19 down to 18 and was obviously still calling for heat. I had to leave it and go to work, not knowing if it would ever hit its 20 deg target yet still keep firing up the boiler. I will know when I get home I guess..lol

    Thanks again
    Wal
     
  6. chris watkins

    chris watkins Plumber

    A water temperature of 50 deg C will not harm the floor (most are designed with a flow of 50) but what you really do need to know is what the actual resulting floor surface temp of the tiles is after a couple of hours, against the air temp of the room.

    Are the two U/F circuits that you switch on the only heating /hot water demand you have first thing only this may not be enough demand for the boiler to fire correctly without cycling?

    You should also remember that just because a boiler is on it may not be using the same amount of gas. In a Rad system you could burn a cubic metre of gas very quickly putting all that heat into the rads for a fast heat up, whereas that same metre cubed of gas would be burnt slowly over a longer period often more efficiently & put into the floor slab to heat the room. Same amount of gas used & boiler will have been on much longer just at a lower rate.

    Hope that helps Wal

    PS Don't leave any babies on the flooring when it is on, they can't control their body heat & tend to cook!
     
    Last edited: Dec 22, 2016
  7. stig125

    stig125 New Member

    Hi Chris,
    That's so good to know.I was worried about having it any higher.

    The demand is only the 2 zones which is a really good reason why this has changed as the HIVE, being all zones as one, would be putting twice as much demand on the system first thing.

    I will measure the floor temp and air temp and see where we are. I could also bring in the other 2 zones on a slightly lower heat requirement to put a bit more load on the boiler.

    Thanks so much for sticking with this, it's much appreciated

    Wal
     
  8. Uheat – Jake

    Uheat – Jake Sponsor

    Hello Stig,

    UFH is designed to be left on at a constant steady low temeperature and slowly release the heat through the screed gradually throughout the day, so if you're wanting to program the thermostats it's best to have a long period of time programmed.

    We recommend a flow temperature of 45 to 50 degrees with an inscreed system, so turning the mixing valve to 50 would be ok.

    Jake
     
    • Like Like x 1
  9. stig125

    stig125 New Member

    Hi Jake,
    Thanks for your reply. Due to the A rated EPC, without any heating, my house runs around 17deg and has only hit 16deg twice since November. I don't mind running it constant during the day but would like it to be 20 for the evening. Would it still be beneficial if I ran it at 17 Deg until 6pm and then to run at 20 until 11pm then revert back to 17? And what sort of time would I need to start the 20 at to make it reach it by 6pm?

    I can put up with 17 in the morning as I'm usually dosed up on coffee and the Adrenalin of dashing around as I've overslept..lol

    Wal
     
  10. stig125

    stig125 New Member

    Hi Chris,
    When I came home the lounge air temp was at 18deg. I raised the flow temp to 50deg and the UFH had just kicked in at 6pm.
    It's now 9pm and the air temp is 19deg. The temperature of the tiles is 26.1 deg (measured by my german made fish tank thermometer taped to the tiles)..lol. I know this is accurate.
    This is after 3 hours. Is this what you would expect for the floor temp? and is only a 1 deg rise in 3 hours ok?

    Wal
     
  11. Tony Kershaw

    Tony Kershaw Guest

    Hi everyone,

    I don't have any advice for Stig, but can agree from experience (with our church hall UFH) with those who have said that UFH needs to be on all the time. In fact, I need to set the temperature to 60 degrees to get any reasonable performance.

    I was interested to see Stig's mention of advice he'd been given about setting a lower pump speed. Our church hall system performs very badly in very cold conditions, and I wonder whether I can squeeze a bit more performance out of it by reducing pump speed?

    Sorry to hijack your post, Stig, but maybe the answer to my question will help you too?

    Tony
     
  12. chris watkins

    chris watkins Plumber

    Hi Tony
    Turning down the pump will not increase the systems performance I am afraid. If you have it up at 60 deg C flow I take it that your flooring can take the resulting floor temperatures? (normally not greater than 26 but should not be more than 29 in occupied areas)

    What is the finish ?
    and do you hold parent & baby / toddlers group sessions?

    UFH is probably not the best choice for a hall which is not used all the time.
    Can only suggest improving the insulation or is it possible to add a couple of LST rads or convector heaters which could be used just to boost the air temperature when the hall is in use. These could be feed from the existing manifolds if there are any spare ways.
     
    Last edited: Jan 3, 2017
  13. Tony Kershaw

    Tony Kershaw Guest

    Thanks Chris,

    I'll leave the pump speed alone then. Floor is vinyl, and yes we have tots - will check the floor temperature, although no complaints about it being too hot. The hall is in constant use, so UFH a good choice probably. But it's a big Victoria stone box, so no hope of insulation. Have been thinking of adding rads though, so that's for confirming that idea.

    Stig - we have our system on 24/7, but 4 degrees lower 10pm to 6am. Any greater difference, and it takes too long to warm up in the morning. Perhaps a domestic situation would handle that better?

    Tony
     
  14. chris watkins

    chris watkins Plumber

    You may want to consider a warning notice regarding babies being left on the heated floor for any length of time, as I understand it young babies have difficulty in regulating their body temperatures so if their are left lying on the floor they can overheat.

    A couple of rads sound the best option off of the manifolds, use a thermostat to control each as a boost when cold.
     
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