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  • FIRST POST
    • BillG100
    • By BillG100 10th Dec 17, 5:32 PM
    • 29Posts
    • 8Thanks
    BillG100
    Vaillant Ecotec boiler losing pressure intermittently
    • #1
    • 10th Dec 17, 5:32 PM
    Vaillant Ecotec boiler losing pressure intermittently 10th Dec 17 at 5:32 PM
    Hi,

    My Vaillant Ecotec boiler is losing pressure intermittently but quickly and only when it is switched off! What happens is...

    1) The boiler runs fine for a period of time which could be a few days or weeks and the pressure is reasonably constant (varies about 10% to 15% with the temperature)

    2) Boiler loses pressure quickly during the overnight period when heating / water is off

    3) Boiler won't restart and an f.75 error code is displayed

    4) I add some water to re-pressurise and it starts again without a problem

    5) The cycle (steps 1 to 4) then repeat

    The expansion vessel has been re-pressurised. There's no sign of a leak and it would have to be an odd one to behave in this way. The pressure gauge reading appears to be correct.

    I'm at a loss. Any ideas?
Page 1
    • Alex1983
    • By Alex1983 10th Dec 17, 5:37 PM
    • 828 Posts
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    Alex1983
    • #2
    • 10th Dec 17, 5:37 PM
    • #2
    • 10th Dec 17, 5:37 PM
    Repressurise the boiler and shut the central heating flow and return valves off and leave it for 2 days, if the pressure goes then the boiler is the source of the leak if it doesn!!!8217;t then you can slowly open the valves and see if the pressure goes straight away, if this happens the the leak is on the heating system.
    • BillG100
    • By BillG100 10th Dec 17, 6:33 PM
    • 29 Posts
    • 8 Thanks
    BillG100
    • #3
    • 10th Dec 17, 6:33 PM
    • #3
    • 10th Dec 17, 6:33 PM
    Repressurise the boiler and shut the central heating flow and return valves off and leave it for 2 days, if the pressure goes then the boiler is the source of the leak if it doesn!!!8217;t then you can slowly open the valves and see if the pressure goes straight away, if this happens the the leak is on the heating system.
    Originally posted by Alex1983
    Thanks but sometimes the boiler runs and maintains pressure for several weeks. How would shutting off the valves for 2 days prove anything? It's also odd that the boiler only appears to de-pressurises when it is off. For example it shows 2bar at 11pm when I go to bed and the next morning it is "flat" and an F.75 error code is displayed.
    • Ruski
    • By Ruski 10th Dec 17, 6:44 PM
    • 1,551 Posts
    • 909 Thanks
    Ruski
    • #4
    • 10th Dec 17, 6:44 PM
    • #4
    • 10th Dec 17, 6:44 PM
    Is the filling loop connected? It could be letting by and then the PRV would activate at 3bar.... I doubt it would 'empty' the system, but it a scenario worth considering and testing for.

    HTH

    Russ
    Perfection takes time: don't expect miracles in a day
    • Alex1983
    • By Alex1983 10th Dec 17, 6:56 PM
    • 828 Posts
    • 491 Thanks
    Alex1983
    • #5
    • 10th Dec 17, 6:56 PM
    • #5
    • 10th Dec 17, 6:56 PM
    It doesn!!!8217;t matter if it!!!8217;s on or off, it!!!8217;s a sealed system if your loosing pressure it has a leak. Weather that!!!8217;s the PRV dripping, a leak under the floor or on the system or the heat exchanger leaking internally. If you don!!!8217;t want to isolate it temporary then the only other thing you can do is tape a sandwich bag over the PRV pipe outside and wait for it to loose pressure then see if there is any water in the bag.
    • BillG100
    • By BillG100 11th Dec 17, 10:39 PM
    • 29 Posts
    • 8 Thanks
    BillG100
    • #6
    • 11th Dec 17, 10:39 PM
    • #6
    • 11th Dec 17, 10:39 PM
    If the heat exchanger is leaking internally how can it be diagnosed?
    • Alex1983
    • By Alex1983 11th Dec 17, 10:45 PM
    • 828 Posts
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    Alex1983
    • #7
    • 11th Dec 17, 10:45 PM
    • #7
    • 11th Dec 17, 10:45 PM
    Not easily, it will go down the condense pipework. Leave it off for a while and see how much water comes out of the pipework, if a constant drip comes out then that!!!8217;s the likely location of the leak.
    • BillG100
    • By BillG100 19th Dec 17, 7:42 AM
    • 29 Posts
    • 8 Thanks
    BillG100
    • #8
    • 19th Dec 17, 7:42 AM
    • #8
    • 19th Dec 17, 7:42 AM
    Still having the same problem. I've stuck a webcam on the boiler pressure gauges (analogue and digital) and record 24x7. Basically what happens is the boiler starts losing pressure as soon as it switches off at night. It falls below the threshold level and can't restart. It displays an F.75 error code. I put some water in and get it going again without problems.

    Diagnosis:
    1) Three British Gas engineers. They ended-up pointing the finger towards the underfloor heating system

    2) Underfloor heating installers came back and took a look. Said all was good BUT to prove it they suggested taking it off the system (with the out and return valves closed off and programmer off so pump wouldn't be going). I have done this three times and the boiler still loses pressure

    3) The rest of the pipework to the few rads we have is visible (nothing under concrete ets) and no damp patches or evidence of them anywhere

    I'm not a heating engineer or plumber but to me the evidence points to a fault with the boiler. The last BG engineer said the condensate pipe was dry so it can't be a heat exchanger issue. However the Vaillant ecoTEC manual says....

    "The ecoTEC plus appliances are fitted with a siphonic trap (The filling height is 145mm). The siphon collects the accumulated condensate in a container of approx 200ml capacity and directs the entire content into the drain pipe. The risk of the condensate drain pipe freezing is thus minimised"

    ...to me that suggests it is perfectly possible that the condensate pipe was dry when the engineer checked it because the water is stored before being purged from the system.

    I've got another BG engineer coming round to investigate further. Any suggestions on how I should take things forward?
    • daveyjp
    • By daveyjp 19th Dec 17, 7:57 AM
    • 7,544 Posts
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    daveyjp
    • #9
    • 19th Dec 17, 7:57 AM
    • #9
    • 19th Dec 17, 7:57 AM
    You may be better calling Vaillant and getting one of their engineers to visit.
    • Alex1983
    • By Alex1983 19th Dec 17, 8:27 AM
    • 828 Posts
    • 491 Thanks
    Alex1983
    Do what I said in post 2 and you will prove where the problem is without all the hassle your having now.
    • BillG100
    • By BillG100 28th Dec 17, 2:45 PM
    • 29 Posts
    • 8 Thanks
    BillG100
    Do what I said in post 2 and you will prove where the problem is without all the hassle your having now.
    Originally posted by Alex1983
    1) British Gas put a new heat exchange in and it made no difference
    2) The underfloor heating was isolated and it made no difference
    3) There's no sign of a leak on the old rads / pipework. I've tried wrapping tissue around the valves, probing the walls with a decent quality moisture detector and using an endoscope on stretches of the pipes not visible. Nothing!

    I will now do your post 2 suggestion (haven't yet because there are others in the house!) although since the heat exchanger has been replaced and the PRV is ok I doubt it can be the boiler.

    Sorry if this is a dumb question but are the central heating flow and return valves on the boiler? If not how do I find / identify them?
    • bris
    • By bris 28th Dec 17, 2:51 PM
    • 7,675 Posts
    • 6,677 Thanks
    bris
    Trace the pipes up to the boiler, there will be 3 22mm valves, 2 for flow and return and 1 for gas. Turn the flow and return off. Make sure its pressurised before doing so.


    P.s don't try and use the heating with the valves closed.
    • Alex1983
    • By Alex1983 28th Dec 17, 3:01 PM
    • 828 Posts
    • 491 Thanks
    Alex1983
    It!!!8217;s unlikely to make any difference, the only 2 places it can leak in the boiler is the PRV and the heat exchanger and seeing as they!!!8217;ve both been done it!!!8217;s looking like a issue on the system.

    How many radiators do you have?
    • Alex1983
    • By Alex1983 28th Dec 17, 3:08 PM
    • 828 Posts
    • 491 Thanks
    Alex1983
    Also might be worth going back to basics and capping the under floor off just in case one of the isolation valves is passing.
    • BillG100
    • By BillG100 28th Dec 17, 3:40 PM
    • 29 Posts
    • 8 Thanks
    BillG100
    Thanks. I've just spoken to Vaillant and they told me an F.75 error is usually a problem with the Pressure Release Vessel rather than a leak in the system which normally generates an F.22.

    I explained there was no sign of water from the overflow pipe so if that is the case where could the water be going. They said the Pressure Vessel (?) holds approx 1 gallon of water and it won't release until full. As I only need to add a small amount of water (a second or two of the tap on) into the system every couple of days it may take a long time to fill.

    Does that make sense / sound plausible? I would have assumed the BG engineer would have checked whether there was water in the pressure vessel but perhaps he didn't. Anyway BG are sending out another engineer (it's on homecare cover or whatever they call it) in a couple of days.

    If the pressure vessel is ruled out I'll then isolate the boiler as discussed above.
    • Alex1983
    • By Alex1983 28th Dec 17, 4:02 PM
    • 828 Posts
    • 491 Thanks
    Alex1983
    Pressure vessel is the expansion vessel which will be charged to 0.8bar of air pressure I think on the Vaillant, it will be printed on the side of the vessel.

    F75 means the boiler tried to fire up but the pressure sensor didn!!!8217;t detect the increase, it means a problem with the sensor/ pump or water pressure. If your topping up a lot your losing water.

    The pressure sensors are temperament when they have dirt in them, I!!!8217;d be surprised if they haven!!!8217;t changed it all ready, you say they checked the vessel and replaced the heat exchanger. This only leaves a leak at the pressure relief valve or on the system.
    • BillG100
    • By BillG100 31st Dec 17, 12:13 PM
    • 29 Posts
    • 8 Thanks
    BillG100
    The latest update to the saga is:

    1) BG seem happy the UH is isolated (valves not passing)
    2) They have now changed the schrader valve on the expansion vessel
    3) They said the pressure sensor (the one which provides data for the digital display) was faulty and have changed it

    Of course even if 2 & 3 were causing problems it doesn't explain where the water was going as the overflow pipe is completely dry!

    If the problem is still present after making the latest changes (will know in a couple of days) they will send the leak specialists in with thermal imaging / inert gas etc.
    • mossy007
    • By mossy007 4th Jan 18, 10:54 AM
    • 8 Posts
    • 1 Thanks
    mossy007
    Can you please let me know how you got on. I have the exact same issues with my same system UFH and CH and losing pressure intermittently some days few days some days overnight. We have had numerous visits from Baxi who have changed PRV and expansion vessel. When PRV was replaced the pressure held for 5 days and then lost pressure, more consistently overnight now. We are tearing our hair out at the moment.
    • BillG100
    • By BillG100 7th Jan 18, 11:37 AM
    • 29 Posts
    • 8 Thanks
    BillG100
    Can you please let me know how you got on. I have the exact same issues with my same system UFH and CH and losing pressure intermittently some days few days some days overnight. We have had numerous visits from Baxi who have changed PRV and expansion vessel. When PRV was replaced the pressure held for 5 days and then lost pressure, more consistently overnight now. We are tearing our hair out at the moment.
    Originally posted by mossy007
    Problem isn't fixed so leak detection are coming in with thermal cameras / acoustics / inert gas. We know the water has to be going somewhere but it is proving very difficult to determine where.
    • vickthestick
    • By vickthestick 8th Jan 18, 7:06 PM
    • 192 Posts
    • 1,526 Thanks
    vickthestick
    Thanks for all of this.
    This is exactly our difficulty as well, minus the Underfloor Heating, but plus leaking radiators once the boiler cuts itself out - they don't leak if the system is pressured up.
    Engineer out to take a looky-see tomorrow.
    Please let us know how you get on.
    Womble #9 2018 0 / Roadkill 0
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