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
-
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.
0 -
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.
0 -
Water doesn't just appear out of nowhere, it's being fed somehow or another. Unplug the feeder and see if it stops.
0 -
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
0 -
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.
0 -
-
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.
0 -
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
0 -
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
0 -
Thank you, for some reason the other discussion didnt show up under "my discussions"
0 -
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.
0 -
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.
0 -
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
1 -
I get air.
0 -
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.
0 -
So is the consensus that the issue has to be either with a leak from the higher pressure supply side or the expansion tank? Are these the only two things that can cause a increase in static pressure like i am observing? There is nothing about the piping arrangement or boiler settings that can cause a continuing rise of static pressure? It isnt that the system is overfilled, or the location of the check valve, or the boiler settings being to hot?
Thank you
0 -
The expansion tank cannot cause an increase in static pressure, unless someone is putting air into it.
Nor can boiler settings. The static pressure is measured with the boiler cold.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
You checked the expansion tank valve and got air, not water, which is good.
But if the tank had too little free volume left for hot water to expand into (say, if the tank were already 75% full of water) you would expect to see the behavior you're seeing, with pressure creeping up as the water heats up. So normally it would be a good idea to isolate the expansion tank, drain it completely, refill it with air to the desired static pressure, and reconnect it to the system.
But since the house is only 2 years old and you are now on a second expansion tank, with the same problem manifesting, it seems unlikely that an over-full tank would be to blame.
1 -
Let me try again. The pressure will rise as the water heats up. If it rises too much — more than say ten pounds — the expansion tank is suspect.
However, if the pressure comes back down again when it cools, it's not the expansion tank which is causing a pressure rise over time.
It is my understanding of the problem that over time the static pressure — the cold pressure — is rising.
If that is so, the only way that can happen is if additional water is getting into the system. Nothing else can do that.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
4 -
static pressure , to me, is the pressure with the circulators turned off.
Dynamic pressure is an indication head has been added by a spinning circ. Depending on where the gauge is located in the system.If the boiler fired without a circ running, you would expect to see the static pressure rise from the expansion of the water
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
You need to be able to shut down the heating loop thru the indirect to rule it out. you need isolation valves on the loop between the boiler and tank. I would say that over 90% of my relief valves discharging when it has the boiler heating an indirect or instantaneous hot water heater is due to the failed coil in the tank. The higher pressure domestic water bleeds into the boiler side of the system and causes the relief valve to discharge.
A failed expansion tank would cause a rise and fall in pressure due to temperature change.
1 -
Quite true. A slightly different interpretation of static pressure — I was using it to be the system pressure with everything off and cold.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Thank you
0 -
Thank you
0
Categories
- All Categories
- 86.6K THE MAIN WALL
- 3.1K A-C, Heat Pumps & Refrigeration
- 54 Biomass
- 423 Carbon Monoxide Awareness
- 100 Chimneys & Flues
- 2K Domestic Hot Water
- 5.6K Gas Heating
- 101 Geothermal
- 158 Indoor-Air Quality
- 3.5K Oil Heating
- 66 Pipe Deterioration
- 934 Plumbing
- 6.2K Radiant Heating
- 384 Solar
- 15.2K Strictly Steam
- 3.3K Thermostats and Controls
- 54 Water Quality
- 43 Industry Classes
- 48 Job Opportunities
- 17 Recall Announcements