First off thanks for any help that can be offered. Our home has hydronic heat, powered by 2 WM HEII boilers, which are about 17 seasons old. They are controlled by a Tekmar control panel with external temp sensor and also make DHW.

The pressure relief valve on the side of one of the boilers was bad and the WATTS autofill was leaking so I replaced them both and the other boiler pressure relief at the same time.

The gauge on one boiler runs about 7-8 PSI higher than the other, and I figured one of the gauges was bad.

Our house is tall, with heat on three floors above the basement where the boilers are, in addition, the boiler is at one end of the basement, so there is a 60' run to the upward turn towards 3 floors. I had been running the system at about 20 PSI to reach the 3rd floor bedrooms.

On either side of the autofill (standard WATTS valve), is a shutoff, and between the autofill and the system side shutoff is a newer PSI gauge which I use to regulate the autofill.

I shut everything down, replaced the autofill and both boiler pressure relief valves. I then closed the valve on the system side of the autofill re-opened the shutoff on the feed side and used the gauge to regulate to 20 PSI.

I then opened up the closed valve on the system side and the autofill ran until the PSI at the autofill was 20, one boiler showed 28 the other showed 20.

I turned on the power, both boilers fired up, and the system fired to a target temp of about 170 and shut off, everything ok..

Went down the next morning during a long cycle (recovering from overnight setback) and one boiler had pushed about 2 gallons of water into a bucket, the other was dry.

I shut off the autofill and let the system run for a few days, assuming it would eventually stop pushing water and "equalize". For about 2-3 days I found less and less water in the bucket under the one boiler, the other dry every morning. Eventually, both were dry for 3-4 straight days.

I shut off the water on the feed site of the autofill, turned off the power to stop the circulators and re-opened the shutoff on the system side of the watts, and the gauge leveled at about 12 PSI.

So it seems like keeping the system at 12 PSI will keep the one boiler pressure relief from tripping (its a 30PSI pressure relief), but my daughter noticed she's not getting heat to the third floor.

The only thing I haven't checked is the pressure vessel, but I'm still wondering why only one boiler is pushing water through the relief valve? Can the new relief valve I just installed be bad? Maybe I should switch them and see if it does the same on the other boiler??

I also noticed that the pressure vessel (which is mounted sideways) gets a little hot but never more than about 5%-10% of the size of the vessel. I would think then the water is HOT, the vessel would be taking up the increased volume and fill a bit and then the water would return to the system when the water cooled? How much does a properly functioning vessel fill, 1/2 way??

thanks!!

Thanks for all help...