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Pressure loss on unvented system with ideal logic boiler advice required

Discussion in 'Plumbing and Central Heating' started by Craggy, 30 Jun 2021.

  1. Craggy

    Craggy

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    Hi,

    I am seeking help on what could be potential faults with my central heating/ hot water system. For over a month it has been losing full pressure after one use. i.e., re-pressurise to 1+ (1.5 bar when on), on long enough to get a tank of hot water and it loses all pressure in that duration, which after a few hours of use the f1 fault again on boiler. (the filling loop seems to take a decent amount of water to re-pressurise too)

    I have not had the central heating on for a while, we have just used it for hot water for a month or more.

    The main components of the system are;

    · Ideal logic plus boiler (7 yrs old) – in downstairs utility (fully serviced, and recently checked for leaks, I am told it is not the boiler at fault)

    · Plumbcentre centre store, unvented cylinder 170 litres upstairs airing cupboard (7 yrs).

    · White aqua system multifunctional tank installed above the 170 litre tank in airing cupboard. No red tank. (there is tiny drip on the pipe to this white tank which has been there for ages, again I am told this is not the issue)

    · Copper pipe, 22m under floorboards to microbore tails to radiators, 30 yrs old.


    From recent investigations by local central heating professionals, I am told that it must be a leak on the central heating system in the house somewhere. We cannot see anything dripping at the radiator connections, and no wet ceilings downstairs. The loss is substantial, so if it is on the heating pipes, downstairs seems the only likely candidate where we cannot see it.


    Some Observations

    · I cannot see any leaks or wet ceilings around the house.

    · There could be a leak under downstairs floor but what might of caused something so substantial out of the blue is anyone’s guess.

    · The copper pipe out of the boiler through the outside wall downstairs (for discharging leaks?) to release water is bone dry when in operation, even after an extended period.

    · When the boiler is on, the overflow pipe I think it is? Out the wall behind the 170 litre tank upstairs drips like a tap, a lot of water. to the uneducated (me) this looks like a big leak.

    · There is no leaks at the tundish? (I think it is called)

    · Radiators have not been bled recently

    · White tank above 170 tank has not been pressurised in over 6 years, but it has not been done at servicing wither when we have fire, cooker, boiler done.


    I suppose what I am asking is, could the external release pipe behind the centre store be at fault for where all the water is going? Basically, it appears to be losing a lot of water. I can see a lot of water dripping out of the release pipe behind the unvented cylinder upstairs to the garden, but I have had two companies out and both say it must be a leak in the central heating pipe system, nothing to do with the pipe to the outer wall upstairs. consequently the internal leak requires infra-red camera hire etc to find it or trying rad-weld type liquids, which I doubt will work. My eyes are seeing it come out like a tap from my outside wall and is there any other conceivable fault, other than a leak under the floorboards?.
    I could upload photos if it would help.

    Any advice appreciated thanks.
     
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  3. Mottie

    Mottie

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    The last thing I would do is use any type of sealer in the system. BTW, I’m not a heating engineer!
     
    Last edited: 30 Jun 2021
  4. ianmcd

    ianmcd

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    yes photos are good so we can see what you have
     
  5. fatplumber

    fatplumber

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    Firstly, there are no overflow pipes. Your unvented has two safety valves. One is pressure only and is on the incoming water main to the cylinder. The other is a temperature and pressure relief valve on the side of the cylinder. Both these should run into the tundish. These tend to run when a service is required. You need to be licensed to work on an unvented. The pipe on the boiler is from the internal safety valve. None of these valves should be leaking. It is possible that you have another safety valve on your heating that has failed. Is there another expansion vessel on your heating? This would usually be red.
     
  6. steve32

    steve32

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    Turn the boiler off, disconnect the condense pipe and put a bowl or bucket under the pipe where it comes out of
    the boiler.
    Pressurise the boiler to 2bar and leave for a few hours and check if there is any water coming out of the condense
    pipe we normally leave it overnight.
    If there is water coming out the heat exchanger is split.
     
  7. Craggy

    Craggy

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    10F65C1C-60F5-47DB-9A51-B191AFC20713.JPG ABD8720D-2BCA-4145-AE46-90D85165D045.JPG D9A91FC2-47EA-4DE5-A898-6027FF5387EA.JPG F8F65943-DB75-4628-9954-1B8D725C9DED.JPG 3C32FB16-644F-46B1-87F8-1C725FC64881.JPG 1EAB11E9-15EB-4EA8-9E6E-4EF31E0E7975.JPG 0DD2337A-3149-43F2-81B0-33BA202C2A2D.JPG IMG-1672.jpg
     

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  8. Craggy

    Craggy

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  9. Craggy

    Craggy

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    hi thanks for the replies, hopefully the pictures help... it is the last picture that the pipe to the outside behind the tank absolutely pees out when boiler is on. i have noted that expasion pressure vessel and heat exchanger test may be things to try before searching any more for leaks.

    i cannot see a red safety vessel anywhere unfortunately. there is nothing in the loft or downstairs. cheers for the description, yes im not too familiair with the exact purpsoe of each part. i looked on gas safe register for unvented ticket engineers and cant find any!

    thanks
     
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  11. Craggy

    Craggy

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    ps, it is the gauge in the bottom left corner of the cupboard that loses pressure, the one near to the tundish is stable.
     
  12. steve32

    steve32

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    The red expansion unit is in the boiler
     
  13. kidgreen61

    kidgreen61

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    Looks like the boiler PRV has been losing water from the green stains on the wall
     
  14. Craggy

    Craggy

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    hi thanks, could that explain the pressure loss in the system? as currently i keep being told that pipe has no effect on pressure, which is what i am doubting, or at least getting a 2nd opinion on
     
  15. oldbuffer

    oldbuffer

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    1. Judging by your photographs, the boiler is in a ground floor kitchen and the unvented hot water cylinder in an upstairs airing cupboard.
    2. If this is the case, then:
    2a. The pressure relief pipework from the boiler should terminate outside at a lower level than the boiler. Assuming you have a reasonably level plot, this would put it about 1 to 1.5 metres up from ground level more or less behind the boiler. It should terminate by pointing towards the wall.
    2b. The pressure and temperature & pressure relief pipe from the unvented cylinder is likely to be the high level one in your final photograph. This appears to have been weeping at some stage. The unvented cylinder will have two devices which require pressure relief. The temperature and pressure relief valve (TPRV), which is the valve with the black plastic knob just above the black plastic tun dish in your photographs is one, the other is a pressure relief valve built into the combination valve which feeds the cylinder with cold water. The combination valve is the valve with the black plastic "top hat" behind the pressure gauge in your photographs. The pressure relief valve is normally attached to the pipework before the tun dish for the TPRV, so that any escape of water from the combination valve is visible at the tun dish. Yours appears (and I cannot be certain) to have been connected to the relief pipework after the tun dish. This would account for the escape of water with a dry tun dish.
    3. Nothing to do with your hot water cylinder can affect the pressure in your boiler, except a leaking primary coil in the cylinder with the boiler pressure higher than that of the cylinder. Highly unlikely, so whoever has told you that "that pipe has no effect on pressure" is correct.
    4. I suspect you have two faults:
    4a. The combination valve for the hot water cylinder is is passing water to the relief pipework. I would advise getting the cylinder and all its components / ancillaries checked by someone with a G3 qualification. I would get the combination valve's pressure relief outlet re-routed via the tun dish at the same time.
    4b. A fault with the boiler and / or central heating / hot water primary circuit.
    5. To check the boiler:
    5a. Run the system to get a decent store of hot water.
    5b. Let the system cool for half an hour, re-pressurise the boiler to 1.5 bar and turn the boiler off.
    5c. Isolate the boiler from the system by closing the valve to the flow and return pipes under the boiler. The manual for your boiler will tell you which valves these are. Note that sometimes these valves leak when used, and if this happens you will have to replace them. They are fairly expensive (£40 to £60 each?) and replacement requires the system to be drained.
    5d. Leave it for 24 hours.
    5e. If the system has lost pressure, the leak is in the boiler.
    5f. Open the flow and return valves under the boiler. Leave for a further 24 hours.
    5g. If the pressure drops, the leak is in the system, either in the central heating, or in the hot water cylinder's primary circuit.
     
  16. Craggy

    Craggy

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    Hi, thankyou very much for the detailed response, this is very helpful and appreciated. this weekends job is to work through what you have suggested and I am currently patiently waiting during step 5d! (the flow and return were stiff and awkward bot seems like no leaks from them yet)

    can i just double check throughout the whole 48 hour test period that i leave the boiler switched off?

    thanks
     
  17. oldbuffer

    oldbuffer

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    Yes, leave it switched off.
     
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