Hydronic overpressure problem

R. Taliano

Hi all
I have a 3 zone hydroair with a Monitor MZ-40 boiler and standard taco circulating pumps. Last heating season I had drainage from my pressure relief drain. First the pressure relief valve was replaced...no improvement. Then the expansion tank was replaced near end of heating season last year...now this year I have the same problem. The difference is that this year I actually did witness the pressure gauge go up to 30 psi and saw the overflow valve work properly. Up to this point nobody had witness the pressure go up. The expansion tank is ok. I spoke with a tech from my contractors company and told him what had been happening. He suggested that I may have a circulator pump with a bad winding that may be not starting up right away. Unfortunately I did not think to check to see what zone was calling for heat the only time I have witnessed the pressure go up too high. This is worse than an electrical problem in a car. Of course by the time the serviceman came out I had to drainage for 2 days. The following morning there was a little over one cup of water there. Does anyone else have any suggestions before I start swapping out circulating pumps?

steve gates

check your automatic feed valve.

hr

The expansion tank

that comes inside those units is fairly small. You may need additional expansion tank size.

hot rod

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R. Taliano

How do I check it?

Pardon my ignorance (learning homeowner). The automatic feed valve is between the the backflow preventer and the expansion tank. If so the serviceman claims to have checked it. Although I can see how one could verify that it will let water into the system, how can one check to make sure it does not have an intermittent problem without changing it?

Thanks
Ross T

R. Taliano

It does have a large separate expansion tank.

Thanks
Ross T.

steve gates

Be sure the system pressure is where it is supposed to be(usually 12# cold) then close the isolation valve. You can also check for leaks this way. Run the system and watch the pressure rise.

You may have a pump to large that will raise presure when it shouldn't. If the gauge jumps up right when the pump come on this may be a part of the problem.

I've also seen large tanks not large enough.

Robert O'Connor_7

why not..

Shut off the feed valve. You then will know if thats your problem....Robert O'Connor/NJ

R. Taliano

shutting of feed valve

Since the systems does have a low water cutoff control, I could close the water feed for a day or 2 and see if the problem disappears?

Thanks
Ross T

Ray Landry

Ross how are you heating your hot water? Do you have a tankless hot water heater connected to your boiler? If so the tankless could have a small leak that is intensified as the water heats up, causing the relief valve to pop. Also 12 pounds of pressure cold may not be enough as someone recomended. you need 1 pound of pressure for every 2.31 feet. so if you mesure from your boiler to your highest convecter that will give you the pressure you really need. Lastly, if you are running 20 pounds cold in your system and upper 20's when it is heated, your air pressure in your tank needs to be set to this amount as well, if it wasn't done one year ago the bladder could be failed and not working properly. Can you give us a name and model number of your expansion tank? also do you have cast iron rads or baseboard heat.

Ken_8

Yup

!

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R. Taliano

More info and update

Ray the system is a 3 zone hydroair. Hot water heating is done separately with freestanding hot water tank.

I did speak with the engineer at my installers place today. I also did witness the pressure go to 30 psi again (with water dump off) while one zone was operating. The expansion tank is Amtrol Extrol model 60 pressurized to 12 psi. The Engineer did ask me the height difference. It is close to 35 feet as the basement has 10' walls and air handlers are in attic of 2nd floor. He also wanted me to check whether expansion tank was connected to supply or return side of boiler. It sounded like he felt that it should be connected to return side and this jives with diagram in owners manual. My tank however is definitely attached to supply side. It is not clear to me why this would matter.

RT

R. Taliano

Tank pressure

Does the precharged pressure mean anything or is this modified by the installer at the time of installation?

Dave Stroman

Check the pressure in the tank.

Dave in Denver

Steve Paul

Hydronic over pressure

I read all of the posts about your problem. They all are constructive and valid. The one thing that would I ask, is what is the position of the fast fill pressure reducing valve? I once saw the lever of a B&G fast fill open slightly by gravity when placed in a vertical position, and cause an over pressure. The cure? we wrapped a piece of solder around it and secured the other end tight to the pipe. End of problem.

Empire_2

Expansion Tank

Should be installed on the suction side of the pump...(Pumping away)Pumps on the supply line will aid in air elimination. Water line should go into the fitting above the tank. I think you may find that your problem lies in the pre-charge of the tank at cold install. If you have a 3 story house, you need more pre-charge than 12psi. Call a good contractor who can solve this problem. PRV could also be the problem, but the service guy should be able to solve this problem!!!!

Kyle Kubs

precharge pressure

Ross - The precharge pressure in your expansion tank should be equal to the lowest pressure in the boiler when it is cold - In your case if you have a 35' differential the lowest water pressure should be 15 psi (the minimum needed to push the water to that height (1 psi/28'' of rise above the water line in the boiler)) If that is so - or it may be set a touch higher...- the air pressure in the expansion tank needs to be equal to that or the air volume in the tank is reduced right from the start since there is higher pressure on the water side. On the expansion tank you will find a valve just like the one on a car tire. check it with a tire gauge and ad a litte air if need be.

Good luck

Kyle

Ray Landry

just make sure when you check the expansion tank pressure that you have it disconnected from the boiler, otherwise you will get a false reading...

Unknown

Ross

What you may be experiencing is a symtom called "Phantom Pressure Rise". What causes it? Most homes that have public water have water metering devices that now incorporate a check valve to prevent reverse flow or backflow of potable water back out to the street. When water is heated by means of the external water heater you have installed and no water using devices are active then the water being heated in that water heater has nowhere to expand.

The pressure reducing valve for the boiler system is usually precalibrated for an incoming pressure of about 50 psi reducing to 12 psi on the boiler side. If due to thermal expansion on the potable water side of that valve, the pressure should rise to say 75-100 psi, then the pressure through the boiler pressure reducing valve can increase and the boiler pressure will rise. Once it rises it will not lower because the PR valve also has a check valve to try and prevent backflow. A simple check of this happening would involve shutting off the water supply to the boiler pressure reducing valve and watching to see if it happens again.

If all is well at that point, then your problem is thermal expansion on the potable water side. A simple fix is to have a thermal expansion tank installed on the cold water pipe near the water heater. This way when the pressure increases due to the water heater operating, the expansion tank will absorb the thermal expansion. This tank is similar to the #60 tank you have on the heating system except it has a lining in the tank to keep it from rusting and is rated for higher operating pressures. Another symptom of thermal expansion would be solenoid valves in washing machines and dishwashers banging on and off.

I live in an Atlantic Ocean coastal community in RI and many of the homes in this area are vacant this time of year. Because of this and the resultant low water usage the local water utility generally runs higher street pressures (100 psi) in an effort to keep air pockets compressed in the water mains so that bacteria will not form. This increased water pressure gets into the house and can't get back out because of the water meter check valve and once again the boiler pressure suffers the consequences. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics

www.burnham.com

R. Taliano

Well nothing can be easy can it?

Ok now I have brushed up on my hydronic physics and it seems that the tank must be the problem. I shut off the water/automatic feeder and within 24 hours I had barely any pressure in the system and a good 16-20 oz of water on the floor. Of course nothing is easy though.... the air valve on the expansion tank is about 1" off the floor and any tire gauge I can find has the head at a 45 degree angle. I can't even get my bike pump on there. Anyway my heating contractor has to come back anyway as I don't have any way to know how much glycol I have lost. The engineer said I should have 30-40% max in there. It is my understanding that glycol has a higher expansion coefficient than just water. I wonder if entire problem goes back to the service tech reducing the pressure in the system last spring?