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Copper cylinder not heating properly

  • 13-02-2023 3:56pm
    #1
    Registered Users, Registered Users 2 Posts: 1,225
    ✭✭✭


    My central heating system is open/vented with a condensing boiler burning kerosene and heating radiators and a copper cylinder.

    The only controls are TRVs on every radiator. 

    The only control on the copper cylinder is a gate valve on the inlet of the heating coil. There is no temperature control on it.

    Over the last week or so I've noticed that the cylinder (gate valve always fully open) is only getting up to about 30 degrees or so and only the top one-third is warm. All radiators are heating normally.

    I've bled all the radiators and found little or no air in them.

    Can anyone give me any advice on what the cause might be?



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Comments

  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
    ✭✭✭


    Not in a hard water area and the gate valve opens and closes without any resistance.



  • Moderators, Home & Garden Moderators Posts: 6,378 Wearb
    Mod ✭✭✭✭


    If you turn off half or all of the radiators, does the heating of the cylinder improve?

    Have you worked on the coil recently?

    Sometimes is difficult to know if the gate in the valve is lifting up properly.

    Did the problem suddenly start without any work having been done on the heating system. Eg. Closing and reopening that valve?

    Please follow site and charter rules. "Resistance is futile"



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    I haven't tried turning off rads but will do it now...

    Absolutely no work carried out recently.

    The problem suddenly started without any work being done on the system.

    I only opened and closed the valve after the problem occurred to make sure it was fully open and operating ok.



  • Moderators, Home & Garden Moderators Posts: 6,378 Wearb
    Mod ✭✭✭✭


    Also see if the return pipe on the coil is close to the feed temperature. You can do this by carefully touching them when heating has been on for a while.

    You could alsi turn up the circulation pump to highest setting for 20/30 seconds to see if that makes a difference to coil pipes temperature.

    Please follow site and charter rules. "Resistance is futile"



  • Registered Users, Registered Users 2 Posts: 3,623 John.G
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    Unlikely to be the problem but check that the circulation pump stays running when the burner stops firing.



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  • Registered Users, Registered Users 2 Posts: 3,974 jimf
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    make sure you have water in the small tank in the attic



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    The pump is always set at 2 (of 3). If I turn it up to 3 it overflows into the f&e tank and then out the overflow pipe. I'm in a bungalow.

    I turned off all rads and left it like that for 3 hours and there was no difference in temps at the cylinder.

    This morning at 10am (heating on 24 hrs), after 15 hours of just three rads and cylinder on, no water taken from the cylinder, the temp at the cylinder was...

    Coil inlet: 54 degrees (I'd expect 60). As a test, I turned on a rad and monitored the temp at the top (inlet end) and within seconds it was up to 60 degrees.

    Coil outlet: 46 degrees

    Cylinder temp at the top 36 (cylinder warm almost all the way down). There's no leaking taps.

    Yes, the pump is on permanently.

    f&e tank is full.


    I've come to a conclusion but I won't mention it yet because I'd like to wait and see if anyone else comes up with the same :)



  • Registered Users, Registered Users 2 Posts: 3,623 John.G
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    Was the boiler cycling on/off very rapidly with no rads on, for those 3 hours?.

    A coil dT of 8C ( 54-46) like mine might indicate a coil flowrate of ~ 10LPM which = 5.6kwh/hr which will heat a 150L cylinder from say 20c to 36C in 2.8hrs so makes no sense thermodynamically, also, overnight with no drawdown of hot water then the cylinder temperature (at the top) should have been within a few degrees of 56C. Again no cylinder temperature rise in 3 hours seems "impossible".

    Is your pump A rated and does it indicate the power in watts, W?. if so very easy to see the flowrate through the coil (all rads off) from the pump curves.

    Afraid, I can't come up with any logical reason for above.



  • Registered Users, Registered Users 2 Posts: 846 stephenmarr
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    A possible blockage in the coil of the cylinder.


    A split coil could be possible but unlikely.



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    That's exactly the conclusion I came to (blockage). Delighted someone else agrees that's it might be the problem.

    At first I suspected the pump but because it will spit out to the f&e tank at setting 3 and the fact that the radiator at the furthest end of the house is at full temperature I concluded that it was ok.

    Although the gate valve at the inlet of the coil seems to open and close ok I reckon the flow is only trickling through the coil.

    We can live with it for the moment and I'll do it in a few weeks when the heating season is over.

    Thanks everyone for the help and I will report back.



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  • My copper cylinder was replaced last year due to a blockage. It was over 20 years old and I had previous problems with sludge in the rads so not that surprising.



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    Yeah, this system is 30 years old. I might combine this job with a flush etc.



  • Registered Users, Registered Users 2 Posts: 1,372 monseiur
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    If I was in your position I would think twice before replacing the cylinder. The new copper cylinders are made of ultra thin copper sheet, the copper is rolled to within an inch of it's life which means a shorter lifespan and very vulnerable to being punctured etc. Instead disconnect your cylinder, remove immersion heater and bring outside, remove all silt that may have built up over the years, this will come out the immersion hole and power wash thru coil this will remove any blockage. Turn cylinder upside down and let it any residual water on the bottom flow out. Connect a water hose to coil and let water flow thru for say 15 to 30 minutes. Disconnect hose and turn cylinder upside down, if water flows out your coil is leaking, if not refit cylinder, should be good for another 30 years.



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    Thank you very much. I will certainly keep your advice in mind.



  • Registered Users, Registered Users 2 Posts: 3,623 John.G
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    Why not, as a first measure, drain down the system below the level of the cylinder coil outlet, won't take much if the cylinder is upstairs, check visually or remove to check that the gate valve is opening fully, if valve proves OK, connect a hose to coil and flush through.



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    I put this on the long finger but now that the heating season is approaching I pulled the finger out and did a power flush at the weekend.

    I'm now seeing incontrovertible signs that there is a break/hole/split in the coil within the copper cylinder. Well guessed/suggested @stephenmarr.

    I have a pimb getting this 32 year old cylinder out and not looking forward to finding a replacement. The connections on any I see online don't seem to be a match.

    Anyway, tell me, are there flexi hoses I can use to connect the new cylinder?



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    Got the cylinder out and did a compressed air test on the coil, yep, it's damaged.



  • Registered Users, Registered Users 2 Posts: 846 stephenmarr
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    @WestWicklow1 not a problem.


    Get yourself a stainless steel cylinder.



  • Registered Users, Registered Users 2 Posts: 1,225 WestWicklow1
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    Already bought an insulated copper cylinder!!

    The domestic water inlet and outlet line up but the inlet and outlet of the coil don't match.

    Is it possible to use flexi pipes here?



  • Registered Users, Registered Users 2 Posts: 846 stephenmarr
    ✭✭✭


    I wouldn't .


    Copper all for all connections for the cylinder



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