Closed Loop Static Pressure Climbing/PRV Releasing
I’m hoping someone can help with a static pressure/overpressure problem I’m having with a closed loop residential hydronic heating system. I have attached a (rudimentary) drawing and some pictures.
The system is a closed loop glycol mix heating approximately 4000 square feet, it is 2 years old and works great in terms of providing heat. The setpoint for the DHW is 130F, and the water is supplied to the heating loops at 115 F. I live in climate zone 7 in Alberta, Canada. The house is 2 years old and slightly better than code insulation wise, it is single story bungalow.
The issue is the static pressure of the system increase slowly over time until the boiler PRV releases (30 psi). The pressure is consistent throughout the loops as confirmed by using a pressure gauge at various points on the supply and return. The pressure seems to rise by a couple tenths of a psi every time the system calls for heat.
I blocked in the water supply (supply pressure is 60- 70 psi) which enters the indirect hot water heater to see if there was a leak at the exchanger. The supply was blocked in for approx. 16 hours and I still observed an increase in pressure in the closed loop system over that period.
The original plumbers who installed the system tried adjusting the expansion tank pressure to no avail. I consulted a second plumber, and they suggested replacing the expansion tank with a larger one. This seemed to rectify the issue however it was in the summer and the demand for heat was quite low, now that we are in the heating season the issue remains.
The system consists of a fire tube boiler, Grundfos pumps x 3 (primary loop, heating zones, DHW loop), zone valves, a hydraulic separator and a feed reservoir/pump.
I don’t understand why the static pressure creeps up continuously and I hoping someone here can help before I call the plumbers again.
Thank you for your time and consideration.
Comments
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How did you "block in" the water supply to the DHW heater? Even if you turn a water supply shutoff valve off, there's still 60-70 psi inside the DHW tank.
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And when you say the PRV releases, do you mean the pressure reducing valve? Discharging water?
If so, and I think that's what you mean. I would say the PRV is adjusted wrong or you have a valve passing water or your water pressure set point on the PRV is to high.
It should be, to start, about 12-15 psi.
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Water doesn't just appear out of nowhere, it's being fed somehow or another. Unplug the feeder and see if it stops.
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pull the x tank and measure the pressure.
does this boiler supply HW?0 -
blocked in the supply, drained the hot water by running the taps
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the glycol feeder is your only make up? no other connection?
can you valve off the indirect htg lines from the boiler to the storage?
known to beat dead horses1 -
the boiler PSV is set at 30 PSI. when the static pressure reaches that it release to the floor and then resets. The boiler is serving the closed glycol mix loop. The only interface between the supply of fresh cold water and the boiler/loop is the heat exchange coil in the hot water tank.
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There seems to be some confusion in nomenclature. Please clarify.
Your Pressure reducing valve is set at 30psi?
And your pressure relief valve is rated at 30psi?
What is the pressure of your system when everything is fully cold?
It seems like you have ruled out an exp tank problem. What is the air pressure in the expansion tank when installed? Is that 12psi as stated on exp tank or did installer change it?
Possibilities include a leak in the DHW tank coil that's now feeding your closed loop. Or a faulty feeder/ pressure reducing valve.
I am not convinced you have ruled out a leak from DHW tank.
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valve off the glycol feeder under the grey air sep / hydro block thing that I can't remember the name for , , ,
is the feeder set to 12/15
known to beat dead horses1 -
Thanks @neilc.
@joodokick, I've merged your duplicate discussions into one here to prevent confusion. Thanks.
Forum Moderator
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yes its the only make up, and its low pressure setpoint is 13 PSI. the only valves on that loop are on either side of the pump unfortunately
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Thank you, for some reason the other discussion didnt show up under "my discussions"
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sorry, there is no PRV, only Boiler PSV.
I don't know the pressure when its cold. I can bring the pressure down to whatever i want by bleeding off glycol, but then it will just rise again.
The expansion tank is at 12 PSI.
I agree I may have not done enough to rule out the DHW. I will try again this week.
The feeder level has never dropped, plus you know when it runs it is outrageously loud.
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The feeder level hasn't dropped since it was full. When we tested it by bringing the loop pressure down below the 13 PSI set point the pump engages and is horrendously loud. I have also blocked the feeder from the hydraulic Seperator for extended periods and saw the static pressure rise regardless.
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Push the valve stem on the expansion tanks in, just for a second. Do you get air or water coming out.
If water comes out, the tank is waterlogged, which will cause pressure to increase as the system warms.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
I think what I'm reading in a slightly muddled way is that the pressure rises … and that there are two ways water at domestic pressure can get in there: a leaking feed valve or a leak in the domestic hot water section. Shut off one and see what happens, then shut off the other one. No other way to test.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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I get air.
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Thanks. The feed goes into the hot water tank (or directly to the cold water manifold/taps). I will trouble shoot the DHW tank more this week.
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