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Vaillant ecoTEC under gassed 14milibar - pipe too thin?

Discussion in 'Plumbing and Central Heating' started by James32, 27 Mar 2019.

  1. James32


    27 Mar 2019
    Thanks Received:
    United Kingdom
    Hi. Got a Vaillant ecoTEC pro 28 combi boiler which is about 10 years old. I had a plumber come today as our boiler continually turns off with a F.62 warning and red light, have to press the flame button with a cross on it to reset and get hot water back. The pressure also continually rises to 2.5 - 3 bar so i've been bleeding a radiator to get it back down (then it goes back up again by itself within a day or a few days, the valves are closed).

    Plumber said the boiler is under gassed and the working pressure max load is 14 millibar, where it should be 16millibar minimum. Solution is I need to get a new gas pipe as he says the diameter of our one is too thin (goes under the kitchen tiles, dining room & living room floorboards to outside). Then the pcb needs replacing.

    Bloke sounds like he knows what he's talking about but just want some more opinions before going further.

    1. There's now a warning label on the boiler. Is it significantly dangerous to keep using the boiler like this? what's the worst likely thing that can happen?
    2. There's pipe visible underneath the boiler running down to the ground. Would replacing this part only do anything worthwhile?

    Last edited: 27 Mar 2019
  2. oldbuffer


    6 May 2010
    Thanks Received:
    United Kingdom
    A. If the pressure rises continually, it could be a number of things, including a slight leak in the secondary heat exchanger, the filling loop letting by (I find the Vaillant built in ones with two grey handles particularly prone to this) or some more obscure problem. It needs to be fixed, because the water coming in has oxygen dissolved in it, and, as the inhibitor gets diluted, the chance of the radiators rusting from the inside out increases. It needs to be fixed, and for that you need a gas safe registered engineer.

    B. Not quite sure why the PCB needs replacing. If it is under gassed, then sorting that out should bring it back to normal performance level without anything else doing, unless there is another problem not yet mentioned.

    C. Did the engineer test the working pressure both at the boiler and at the meter? If the meter / governor is faulty, no amount of new pipe work will get the pressure at the appliance back up.

    D. In response to you questions:
    1. The danger is principally to the boiler rather than to people, given that the boiler is a room sealed appliance. If otherwise in good order, the products of combustion should not enter living space. However, the boiler itself can be damaged, and if there are flue faults or casing faults (which you might not know about) there could be a danger to people / animals. Better not to use it until it has been re-checked and fixed.
    2. The size of gas pipe at the boiler isn't the issue, its the ability of the pipe from the meter to the appliance to carry the requisite amount of gas without undue pressure loss (max. 1 mbar drop) which counts. This ability is a function of the length of run and the number of bends / junctions as well as the diameter of the pipe. Because gas is compressible, it is possible to make a gas run up from different diameter pipes, so, if you have to increase the pipe size, you might get away with increasing only the pipes under floorboards (which presumably are accessible, at least to a degree). The size of pipe required can, and should, be calculated, not just done on a "suck it and see" basis.
    • Like Like x 1
  3. ianmcd


    15 Aug 2010
    Thanks Received:
    United Kingdom
    you need a more experienced gas engineer
  4. The F62 error code can be a pcb fault as it is a delayed shutdown of the gas valve. It can also be something else that equates to that failure. Listen to old buffer as that is a highly experienced answer. The rising pressure should also be relatively easy to check - but needs sorting ASAP.

    You may wish to consult another engineer, or you could ask hime/her to recheck their work.
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