Pressure valve leak

Ukrlotus

Hi,  I have 4 zone baseboard heating using gas boiler and domestic hot water heater. In addition I installed about 750 feet 3 loop radiant heating. I am not sure if this is coincidence or one of the components has failed (expension tank, fill valve) because I have leaking pressure valve. All system using same (one) expansion tank and one water fill valve (bell shaped with lever). My expension tank is 12 years old. Do I need to upgrade to larger expension tank or replace the existing 30 extrol tank. My radiant heating operates at 125F. When radiant zone T calls for heat sometimes boiler runs hot and shuts off because of aqua stat high limit. What should I do? Upgrade to bigger expansion tank or replace existing tank. Maybe I need new fill valve or better design for radiant heat. Thank you.

mattmia2

What kind of boiler is it? Does a safety lock out on the boiler or it set an error or is it just the aquastat on a conventional boiler reaching setpoint?

Jamie Hall

It is not clear. Is this just one system, with the radiant heat tied into the domestic hot water? Or is the problem just in the radiant heating system and its boiler?

Ukrlotus

The boiler is Utica with aquastat that has high limit cutoff. 4 zone baseboard (one pump) and 5th zone radiant ( second pump) heat are operated by boiler. In addition I have one hot water tank. All of it connected to one expension tank. I have another post here where I posted pictures. I am not sure how to link it. Thanks

Jamie Hall

I'm still trying to figure this out. What you are saying is that you have a boiler, four heat zones, a radiant zone, and a domestic hot water tank (not heated separately) all connected together with one expansion tank for the entire system.

I hope that's not true. I hope the domestic hot water is not connected to the heating system, and that the heating system has one and only one pipe connecting it to your domestic cold water, with a pressure reducing valve and at least a shutoff valve.

Please try to clarify.

Ukrlotus

Hot water tank is heated separately. Yes it has only one cold water pipe.

mattmia2

So you are trying to figure out why the relief valve is opening?

What are the pressures with the system cold and with it hot?

Jamie Hall

Ah. Forward progress. I suspect you may have two different problems here. On the pressure, the cold system pressure should be around 12 to 15 psi. No more. When the boiler fires and the system heats up, it may rise to as much as 20 psi, but it should not go above that. If the system cold pressure is too high -- particularly if it rises -- there is something amiss with the pressure reducing valve. Try bringing the system pressure cold to 12 psi and then closing the valve on the cold water feed to the system. It should hold. If it does, open the valve -- it shouldn't rise or if it does, to no more than 15 psi and hold.

Now. If the system pressure rises when hot to more than 20 psi or so, there are three possibilities -- all relating to the expansion tank. The simplest is that it doesn't have the right precharge. Again, let the system cool and using a conventional tire gauge, measure the air pressure in the expansion tank. It should be the same as the system pressure. If it's low or zero, there's a precharge problem. If water comes out of the Scharder valeve, the tank bladder is shot and the tank must be replaced. I don't see a handy shutoff valve on the expansion tank, so it will be difficult to actually properly check the precharge. It may also be that the tank is just too small.

Now on the boiler shutoff problem -- that's usually because there simply isn't enough water flowing through the boiler. I'm slightly puzzled by what appears to be a shutoff valve -- closed -- on one of the two feeds to what I take to be the mixing valve for the radiant manifold?

Ukrlotus

Ok, yes indeed forward progress. Eliminated pressure reducing valve(bell Shaped with lever). After testing it pressure holds between 10-12 PSI cold. Radiant system valve is opened now. The picture was taken right after 5th zone installation. However you might be right about not enough water flowing through. Grundfoes alpha 2 circulating pump is set to auto and usually produces about 1 GPM but I can set it up for higher flow. I will wait till end of the season to test expansion tank. However during testing I notice that when boiler kicked in, Boiler PSI went from 10-12 to 15-16 and pressure relief valve start leaking. I did not have this issue prior 5th zone radiant heat installation. Is this coincidence that pressure relive valve went bad at the same time. I replaced pressure relieve valve about 3 years ago. It shouldn't be leaking at 16PSI.?

Jamie Hall

It is not at all unusual for a pressure relief valve to start weeping at well below the set pressure once it has been operated. You could try opening it manually to full flow to see if there is some crud caught in the seat -- but it may need replacing.

Ukrlotus

Thank you for your guidance. I will replace pressure relieve valve but do you think I need to up size of expansion tank after I added 750 feet of radiant tubing to the existing system?

Jamie Hall

You may not need to increase the expansion tank. The pressure swing you are seeing is quite reasonable and unless the pressure relief valve is leaking badly enough to keep the hot pressure low, it seems OK. Now if you have a good pressure relief valve, and the hot pressure goes too high -- say over 20 pounds, then yes. You do.