Should a raditor still be cold after being "on" for 10 hours?

Discussion in 'Plumbers' Talk' started by Jacob Newby, Dec 3, 2021.

  1. Jacob Newby

    Jacob Newby New Member

    We've moved into a small new build studio flat (5th floor of 7) two weeks ago and noticed that, despite the insulation quality, the flat was still chill.

    On inspection we realised that the bottom half of the 2 radiators were cold despite the heating system calling for heat constantly from 06:30 to 22:30 (thermostat set to 22 degrees)

    The highest we've managed to get the flat is 20.5 degrees, and that was with the oven on.

    When we managed to get the builders round to inspect the issue they said "the radiators should be cold on the bottom, because the flooring is cold" and "the radiator will heat up slowly because you've not set the thermostat high enough. Set it 35 to make it heat up quicker."

    Now, I'm no expert but I've used enough radiators to think that sounds like absolute nonsense.

    Can anyone confirm my suspicions, and shed light on what's actually going wrong?
    Last edited: Dec 3, 2021
  2. oldsch00l

    oldsch00l New Member

    That is absolute rubbish from the builders on both counts - a cold floor would not cause the radiator to be cold and the thermostat setting has absolutely no bearing on how quickly the rads heat up.

    I'm assuming these are standard water-fed rads connected to a gas boiler, rather than electric storage heaters or anything like that?

    It sounds like you may have sludge in the radiators (if it was trapped air, the tops would be cold) - but then again that would be very unusual in a brand new installation.

    If your radiators have either standard or thermostatic valves, are these fully open?

    Also check the boiler to see what the radiator output temperature is set at - should be ~75 deg.
  3. Jacob Newby

    Jacob Newby New Member

    Thanks for clarifying that oldsch00l.

    Yup, both standard water-fed radiators. I had heard about 'sludge' but also thoguht it seemed odd on a brand new system.

    One is the control (or something like that) in the main room, so that doens't have the thermostatic valve. The other does, both are set to maximum.

    Hmm, the boilers a bit more confusing as it's a London new build so the whole complex runs off one boiler. I think it's telling us it's it 53 degrees, and it's leaving the system at 32 degrees? I don't think we've got any way to control the boiler tempreture?
  4. quasar9

    quasar9 Screwfix Select

    Not familiar with centrally supplied systems, but looks like the temperature of the incoming water is low for the size of the radiators plus the flow rate maybe poor too. Are the lock shield valves (on the other side of the thermostatic valves on rads) open.

    how do you control your heating ? Is there a thermostat on the wall and do you have your own pump ?
  5. oldsch00l

    oldsch00l New Member

    Ah ok, so it sounds like what's termed a "district heating" system then... it could well be that it is using an air source heat pump rather than a gas-fired boiler. In which case a temp of somewhere in the region of 35 to 45 deg C is what you'd expect for the heating output. Because of this lower output heat pumps can’t deliver heat as quickly as gas systems and require a bit of a change of mindset in terms of how they're used. They’re ideally used to heat your home up slowly over a longer period, and will often require larger radiators to achieve the same level of warmth as a gas system.

    All that said, your rads still shouldn't be colder at the bottom - I suspect a flow rate issue rather than sludge given the age of the property.

    Either way, it is something the builders need to address - don't accept their bullsh!t about cranking up the thermostat!

    Have a look at this post, sounds similar to your issue...

    Good luck!
  6. Jacob Newby

    Jacob Newby New Member

    Thanks for the response quasar9. Lock shield valves (which i'd never heard of until a couple hours ago) are open, one of the radiators is 'warm' here the other is 'cold' here.

    We've got a digital thermostat in the room, which we can set to call heat (i think that's the term?) we've got it set to always be on to try and raisie the tempreture a little.
  7. Jacob Newby

    Jacob Newby New Member

    Thanks oldsch00l, will check it out :)
  8. quasar9

    quasar9 Screwfix Select

    I am guessing that your thermostat controls a valve that allows the supply of hot water into your system. Normally these valves are either on or off, on when thermostat is calling for heat and off when it’s not. There is no in between settings. Turning up the thermostat will have no impact as you have found out already. There must be another valve elsewhere that limits the flow to your flat (so that all flats get roughly the same ) and perhaps this needs to be adjusted.
  9. Mike83

    Mike83 Screwfix Select

    The district will probably heat your system indirectly via a heat exchanger. There is other methods though.
    But if it is feeding it indirectly then the heat exchanger may not be getting enough primary flow. If there’s not enough flow then the heat exchanger will disperse the heat quicker than it can heat up.
  10. Jacob Newby

    Jacob Newby New Member

    Thanks for all the suggestions guys, turns out the exit pipe/tube on the radiator is really really small and had been blocked - another dude pressured through it and we've got heat.
  11. oldsch00l

    oldsch00l New Member

    Great news, glad you're sorted Jacob!

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