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Pressure drop/combi boiler
I recently installed the Weil Mclain Aquabalance WMB 120 gas combi boiler. The issue I have is the dropping of pressure at idle times. When the system runs, it does so a 20psi. When the unit sits idle for a few hours the pressure gauge on the unit drops to near 4 psi. At 8 psi I get a low pressure fault code and the unit will not supply domestic hot water. When there is a demand for heat, the gauge pops up to 20 psi and unit begins to operate, DHW operates. There is no obvious signs, water leakage, in the system. The system, located on the first floor (720 sq. ft.), consists of two loops, first floor, second floor. Two zone valves, one Taco 007, one expansion tank, one spirovent and one Watts water pressure feed valve (15 psi). 3/4 inch oxygen barrier PVC and slant fin baseboard. The unit is set to operate at a high of 158 degrees. Can anyone explain this? I would assume, that if there was a leak, my system would only be filling to 15 psi, limit of water feed.