Hot water not very hot

Discussion in 'Plumbers' Talk' started by big_bad_bob, Nov 15, 2005.

  1. big_bad_bob

    big_bad_bob New Member

    Been having some problems with the hot water recently. The radiators get nice and hot, but the hot water struggles to reach temperature - last night the radiators had been belting away for nearly 2 hours but the water in the cylinder was luke warm. If I turn down the wall thermostat so that the radiators go off it takes at least an hour to get a tank of hot water (feels about 50 degrees).

    I thought it was a dodgy motorised valve, so I fitted a new one, but no difference. The motorised valve is doing its job - I can see it turning between HW, both, CH as I turn the stats. The tank stat is set at 60 and seems to be working OK. There are no loose wires in the control box. Pump is new last year (circulating pumps - set on 3). Boiler service less than 12 months ago and seems to be doing a good job - set just above 3 (of 5) and the water going into the pump is red hot.

    When the pump is supplying the HW and CH the pipes into and out of the cylinder are both very hot, but there doesn't seem to be much heat exchange going on. Could it be scale on the coil - it would be about 20 years old? Don't think there is any air in the system - its been well bled. I can't say how long this problem has been going on - we've only been in the house a year, and relied a lot on the immersion last winter.

    Coil is fed in 22mm, dropping to 15mm on the way out, then there is a gate valve - what is that for? It is pretty much fully open.

    Sorry for the long post - I hope I've included everything.


  2. Walterfilter

    Walterfilter New Member

    If as you say last night the CH was on for 2 hours together with HW, the MV is functioning correctly then sounds like you have a scaled coil...time for a new cylinder..

    The gate valve is likely to be for a bypass - so should remain open , it'll link the flow to the return quite possibly including you bathroom rad within the bypass..
  3. big_bad_bob

    big_bad_bob New Member

    Thanks waterfilter. Is a scaled coil a common problem? - I suppose our water is fairly hard...

    What make of cylinder would people recommend?

    The gate valve is between the coil outlet and the retun pipework. There is another gate valve teed off from just above the pump going to the return pipework, which I was assuming was a bypass?
  4. britishblue

    britishblue New Member

    If it's a scaled up heating coil the performance will have deteriorated slowly over time. If this has happened suddenly it is unlikely to be scale on the coil.

    Had a similar problem recently where the pump was pumping downwards, so that sometimes it got an airlock and the water didn't heat. Is there a air bleed valve on the pipework that goes to the top of the heating coil? If so try unscrewing this slightly to release any trapped air.

  5. heatyman

    heatyman Well-Known Member

    The cause of a similar problem I had was that the scale in the cylinder, not the coil, was covering most of the coil. This may explain why the immersion works as it only heats the top of the cylinder.
  6. britishblue

    britishblue New Member

    Hi heatyman

    Where does big bad bob mention an immersion heater.

  7. big_bad_bob

    big_bad_bob New Member

    Thanks for the suggestions guys. I don't think the problem is air - there are a couple of little air vents in the pipework either side of the pump, and I have bled them.

    The problem is, BB, I don't know if its a gradual loss of performance or a sudden one - as you say, scale would build up slowly, but we've not been in the house that long.

    I suppose if I pop out the immersion heater I'll be able to see down inside with a torch and see if the coil is scaled?

    If I do need a new cylinder, are the SFX ones OK?


  8. big_bad_bob

    big_bad_bob New Member

    BB - I'll check the direction of the pump, but I think it is in the right way round (is that what you mean?). The pump was fitted by a pro, so it must be in the right way round ;) ...... Actually, my mum lived for years with a pump in the wrong way round - it was only when it wore out and someone else replaced it that we realised the original installer didn't know his @rse from his elbow. Amazing how much better the rads performed with the pump the right way round.....

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