GSHP UFH side pressure rising

frslam
frslam Posts: 11
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edited 23 January at 2:39PM in Heat pumps
Hi guys, could do with some advice. I have an IVT HT PLUS E7 (seperate hwc). The ufh side is usually set at 1.5 bar. The needle does go up to around 2 bar when the heatpump is heating the dhw side. Get's really scary like tonight when it's on the legionella cycle and the water's going above 60c to 65c. I have to reduce the pressure from the heating side incase something bursts - it goes past 3 bar (same reading on ground floor manifold guage). I've had to take the pressure back from 3 to 2 bar 3 times tonight by releasing water from the circuit but it kept climbing. Struggling to work out how this could be happening, my only thoughts are, the 3 port valve might not be sealing the supposedly closed side when heating the water, no air comes out when I open the circuit to bleed some pressure out. Why would the heating circuit pressure rise by 2 bar when the domestic hot water's being heated to 65c? Many thanks

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  • Strummer22
    Strummer22 Posts: 593
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    edited 23 December 2023 at 8:28AM
    frslam said:
    Hi guys, could do with some advice. I have an IVT HT PLUS E7 (seperate hwc). The ufh side is usually set at 1.5 bar. The needle does go up to around 2 bar when the heatpump is heating the dhw side. Get's really scary like tonight when it's on the legionella cycle and the water's going above 60c to 65c. I have to reduce the pressure from the heating side incase something bursts - it goes past 3 bar (same reading on ground floor manifold guage). I've had to take the pressure back from 3 to 2 bar 3 times tonight by releasing water from the circuit but it kept climbing. Struggling to work out how this could be happening, my only thoughts are, the 3 port valve might not be sealing the supposedly closed side when heating the water, no air comes out when I open the circuit to bleed some pressure out. Why would the heating circuit pressure rise by 2 bar when the domestic hot water's being heated to 65c? Many thanks
    It must be the valve. The only way a supposedly closed (or vented) system could overpressure is from the DHW side.

    I guess a faulty filling valve could the culprit but it would fill constantly in that case.
  • All the filling valves I have ever seen in any context have a length of metal flexible hose with a valve at each end which I think you are supposed to detach when not in use, although nobody ever does.  So if you have one of those you can detach it and see if it leaks.  
    Reed
  • frslam
    frslam Posts: 11
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    frslam said:
    Hi guys, could do with some advice. I have an IVT HT PLUS E7 (seperate hwc). The ufh side is usually set at 1.5 bar. The needle does go up to around 2 bar when the heatpump is heating the dhw side. Get's really scary like tonight when it's on the legionella cycle and the water's going above 60c to 65c. I have to reduce the pressure from the heating side incase something bursts - it goes past 3 bar (same reading on ground floor manifold guage). I've had to take the pressure back from 3 to 2 bar 3 times tonight by releasing water from the circuit but it kept climbing. Struggling to work out how this could be happening, my only thoughts are, the 3 port valve might not be sealing the supposedly closed side when heating the water, no air comes out when I open the circuit to bleed some pressure out. Why would the heating circuit pressure rise by 2 bar when the domestic hot water's being heated to 65c? Many thanks
    It must be the valve. The only way a supposedly closed (or vented) system could overpressure is from the DHW side.

    I guess a faulty filling valve could the culprit but it would fill constantly in that case.
    Thanks. I always have the valves at both ends of the filling loop closed off when I'm not topping up the system. I'm guessing the increase in pressure from heating the DHW  is leaking through the 3 port valve into the UFH side?
  • QrizB
    QrizB Posts: 13,685
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    frslam said:
    Get's really scary like tonight when it's on the legionella cycle and the water's going above 60c to 65c. I have to reduce the pressure from the heating side incase something bursts
    Any properly-engineered sealed system that's heated should have a pressure relief valve (PRV) that opens and vents before anything bursts (it might even be a legal requirement). This PRV should be checked periodically, usually as part of your annual service.
    Does your system have a PRV? Is it marked with the pressure it opens at?
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
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  • frslam
    frslam Posts: 11
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    QrizB said:
    frslam said:
    Get's really scary like tonight when it's on the legionella cycle and the water's going above 60c to 65c. I have to reduce the pressure from the heating side incase something bursts
    Any properly-engineered sealed system that's heated should have a pressure relief valve (PRV) that opens and vents before anything bursts (it might even be a legal requirement). This PRV should be checked periodically, usually as part of your annual service.
    Does your system have a PRV? Is it marked with the pressure it opens at?
    Thanks. Been thinking about this some more. If the 3-port valve was the issue, the heat would increase as well as the pressure on the space heating side of the system. The only other thing I can think of is a duff expansion vessel on the underfloor heating side. I think I'll get my foot pump out, reduce the pressure of the water in the system then increase the pressure in the expansion vessel
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