Pressure Problems w/Old (Converted?) Gas Hot Water Heating System with Old Compression Tank

casette

Hi all. I have been having some pressure issues with my gas, hot water, heating system. I had service company come out and look but I think they misdiagnosed the issue, and we are now bracing for a huge storm here in NY.

The system is older, and has 2 zones (call them zone 1 and zone 2). Zone 1 is older and covers almost the entire home (approx. 2200 sq. ft) with 9 radiators. This zone/system may have been converted from a steam system (or perhaps an old gravity system, or both) at some point, and uses large cast iron pipes (think they are 2.5", may be 3") that hold a lot of water. Zone 2 is newer, uses standard (3/4" I think) pipes and covers two additions (approx. 700 sq. ft. total) that were added to the home in the early-mid 90s. Zone 2 uses baseboards, not radiators. The two zones have (I believe) different outgoing and return lines from the boiler (i.e., they seem to be completely separate, not one unified system/line controlled by a zone valve). They also seem to operate completely independently - that is, when zone 1 is heating, zone 2 is not, and vice-versa. I have an old style compression tank (maybe 4 foot long by 1 foot diameter, not sure) rather than new style expansion tanks.

The problems I have are, I think, with zone 1. The issue started when I found the pressure relief valve (30 psi) on my dual auto fill valve was leaking. The service company said they thought the valve was leaking because I had a bad/leaky autofill valve, which would of course raise the system pressure to an unsustainable level (EDIT: this is what the tech said, but his supervisor disagreed). However, I did not replace the valve and I do not think that is the problem. Instead, I had the relief portion of the dual valve plugged, which I understand is OK as I have a second, standard pressure relief valve (30 psi) on the boiler and I do not need 2 of these. I also had my compression tank drained.

Once that was done, I turned off the water supply to the autofill valve and observed the system for a few days. What I have found is that when zone 1 is operating, the pressure increases from about 10-15 psi (cold) to about 30 psi at 140 degrees. My aquastat is set to a high limit of 180 degrees, so of course the (remaining) pressure relief valve is tripped after zone 1 exceeds about 140 degrees. So I do not think my issues is a leaky autofill valve as the pressure still increases past the appropriate lever even when the outside water supply is turned off.

Zone 2 has generally been operating fine, except I may have inadvertently lost some water from that system after tripping the pressure relief valve with zone 1. That is, I have heated zone 1 past 140 degrees/30 psi, tripping the pressure relief valve, and then shut off zone 1, at which point zone 2 starts heating and trips the valve as the pressure is still a bit over 30 psi (usually if I shut off zone 1 and only zone 2 is heating, the pressure decreases but does so slowly).

My questions are as follows:
- I assume my issue is with the compression tank as the problem is not with the autofill valve, do you agree? Is it a bad tank or perhaps the tank not being sized properly? Or given the size of the system and the 2.5"/3" pipes, is it to be expected that given the volume of water the pressure will always run high so I should instead set a lower high limit on the aquastat, like 140 degrees? Unfortunately I cannot do this with my current aquastat as it just has a hi limit, and then just 180-240 degrees.
- If I lose water in zone 2, is there any way to fill it in that zone only? I came home the other day and the pressure was running very low when hot, maybe lower than 10 psi. So I opened the autofill valve a bit and let in some water. I just asked my wife and she said it was about 10-15 psi when at 190 degrees, which also seems low (I think it should be more like 15-20). I have shut off this zone for now.

Thanks in advance for any responses.

Tinman

Sounds like you plugged a backflow preventor, and not a relief valve? Can you post a picture? Either way, neither should be plugged.

Did the technician confirm that your tank is not waterlogged? Sounds like it is. There's not much that can wrong with a compression tank. It's just a steel cylinder and it sounds like it's sized properly.

If you lose water from either zone, the entire system loses water. Same as fill, when filling you're not just going to fill one zone without filling the other unless you're pushing water through just one during air purging.

Are you new to this home?

Tinman

https://heatinghelp.com/systems-help-center/why-compression-tanks-waterlog/

If you wander off The Wall, you'll find this.

casette

Stephen Minnich said:

https://heatinghelp.com/systems-help-center/why-compression-tanks-waterlog/

If you wander off The Wall, you'll find this.

Thank you for your response, I did see this before. However, the tech drained my tank so I assumed this was not the issue.

I have been in the home for about a year and a half.

I do not have a picture handy but it looks like this, and is a Watt. It is not a backflow preventer, I do not have one (though would need one if the valve is replaced).

http://shop.4thaveburner.com/store/p/170-Watts-T1450F-Dual-Pressure-Feed-Relief-Valve.aspx

Tinman

What is the BTU input of your boiler?
Are there automatic air vents in your system?
Where is the expansion tank in relation to the pump?
Make and model of pump?
I assume if there is a valve in the pipe to the tank, it is open?

Jamie Hall

The expansion tank may not be waterlogged -- but may well not have enough air in it. It shouldn't need to be prepressurized (unlike bladder tanks), but it needs to be completely empty before the system is pressurized. Ideally, it will be no more than half full when the system is hot. The trick -- as the referenced article notes -- is to keep it that way.

casette

> @Stephen Minnich said:
> What is the BTU input of your boiler?
> Are there automatic air vents in your system?
> Where is the expansion tank in relation to the pump?
> Make and model of pump?
> I assume if there is a valve in the pipe to the tank, it is open?

Thanks again. Responses are below:

1. Not sure, will need to confirm later (on my way home now)
2. I don't think so
3. Pump is behind the machine, connected to what seems to be the return. Tank hangs from ceiling, connected to what seems like the outgoing line. I understand this may be poor placement.
4. It's a large B+G 1/6 HP, 115 volt, 2.85 amp, 1725 rpm, 60 cycles
5. Yes, the valve is open. I also opened and closed it a bunch of times in case it was stuck. FWIW, the pipe to the tank does not get very hot when the system runs at hi temp, not sure if this indicates there is no transfer of the hot and cold water.

Tinman

You may have more than one thing contributing to this. Your tank may be undersized depending on Net BTUH of your boiler and amount of water in the system? Having a B&G HV (2 bolt) circ pumping toward the tank doesn't help either.

casette

If it makes a difference, the input BTU/hr is 175000

EBEBRATT-Ed

Shut the boiler off. Close the valve between the boiler and the expansion tank and shut off the city water make up valve. Drain the expansion tank. Some tanks have a tank drainer fitting to let air into the tank to assist with draining.

Once you get the tank drained. Adjust the water pressure in the boiler to 12-15 psi either by adding water or draining water from the boiler.

Keep the burner and the pump off. crack open the valve between the boiler and the expansion tank and you will here water rushing into the expansion tank. add water to the boiler until you get about 12 psi.

give it a few minuets to settle out. Open the valve between the boiler and the expansion tank all the way. Start the boiler up and return your feed water valve to normal

Tinman

Based on what he has already said, cold fill is 15 and tank has already been drained.

casette

> @EBEBRATT-Ed said:
> Shut the boiler off. Close the valve between the boiler and the expansion tank and shut off the city water make up valve. Drain the expansion tank. Some tanks have a tank drainer fitting to let air into the tank to assist with draining.
>
> Once you get the tank drained. Adjust the water pressure in the boiler to 12-15 psi either by adding water or draining water from the boiler.
>
> Keep the burner and the pump off. crack open the valve between the boiler and the expansion tank and you will here water rushing into the expansion tank. add water to the boiler until you get about 12 psi.
>
> give it a few minuets to settle out. Open the valve between the boiler and the expansion tank all the way. Start the boiler up and return your feed water valve to normal

Thanks, I will try this tonight. I can add water to the boiler manually by lifting the lever on the auto fill valve, right?

casette

> @Stephen Minnich said:
> Based on what he has already said, cold fill is 15 and tank has already been drained.

Yes, should be. I came home today and unfortunately my wife left the system on, when I arrived zone 1 was at 180 degrees and 30 psi with the relief valve tripped and water on the floor. I turned the system off and it is now 10 psi at 160 degrees. I am getting nervous about low pressure as I know as it gets down cooler the pressure will reduce, hopefully the auto fill valve will do its job but...

If it makes a difference the heater is a slant/fin Galaxy gg-175-hp.

EBEBRATT-Ed

Everything your saying points to a waterlogged expansion tank that needs to be drained

hot_rod

just because he drained it, doesn't mean it didn't waterloo when he refilled. Does it have a sight glass on one end. If you rap it with your knuckles you can tell, hear, where the water level is.

Was an automatic air purger installed in the system somewhere ever? You have an air management type of system, no air vents should be installed unless the vent into the compression tank.

Some excellent reading here about the various types of expansion tanks. Thanks to Amtrol for this info share.

EBEBRATT-Ed

@hot rod thanks for the Amtrol. Good stuff

hot_rod

EBEBRATT-Ed said:

@hot rod thanks for the Amtrol. Good stuff

It's a good read. It is the first time I have seen sizing of the expansion tank line explained.

casette

Just want to say thanks to everyone for their responses. I drained the expansion tank as recommended (big thanks to @EBEBRATT-Ed for the excellent instructions) and that seems to have done the trick. Like @hot rod said I think the tech may have waterlogged the tank again when he refilled it. Anyway, many thanks again! Really appreciate the help.