Advice on recurring high pressure, suspecting fill water valve leaking

John B Fowler

Hello All,

My layman’s suspicion: The closed system fill valve is not shutting off completely allowing pressurized fresh water to slowly but continually enter the system.

System: Natural gas fired, 1947, cast iron boiler, single pipe, mono flow, w/cast iron radiators, closed system by American Standard (Empire Model) with a Grundfos pump on the main return line. Newer though 30+ year old gas valve/pilot control. Vintage Honeywell round heating only thermostat. 7” flu vented into adjacent basement-through-roof single flu gas-only clean chimney.

Background: We’ve been in this 1947 insulated home since winter of 1994. Two stories with 3 un-valved radiators in the basement where the boiler is located, 5 un-valved radiators on the open first floor and 3 hand wheel valved radiators in 3 BRs and 1 un-valved radiator in the bathroom on the second floor. The hot water for bathing and cleaning is from a separate gas water heater. The expansion tank is the same vintage, a long overhead single chamber steel unit with a bottom drain plug. Basement ceiling finished so can’t tell if a vent on its top but not rusty and no leakage. I leave the 2 burner pilots on during the off season to avoid condensation/rusting on the boiler and racks and set the valve lever to the summer vice winter position. I do my annual cleaning of the burner racks and observation of the thermocouple for which I keep a spare on hand and change out periodically. I check/bleed air from each of the radiators starting from the basement each fall, usually none in the basement and first floor with only small amount of air in the second-floor units. The PSI gauge fixed pointer has been set for 11 since we’ve been here and likely 1947.

So: Last week as I switched her back to winter position and was getting her started up for the season, I noticed some small steady dripping from the 30lb boiler relief valve down pipe onto the floor and that the moving pressure needle was at 30 indicated. The city water feed valve to the boiler was closed as normal. City pressure is 48-50. I put a pan under the drip and was catching about a gallon every two hours so I suspected the 30 plus year old Watts relief valve was due for replacement. I shut off the power and the gas, let the temperature drop to the minimum shown on the gauge 80 degrees and then opened the relief valve to lower pressure, loosened the plug in the compression tank and drained down the system via a hose on the drain valve to the nearby floor drain. However, it continued to drain and drain although very slowly for hours even overnight. It never actually stopped draining. I installed the new matching Watts relief valve, noted the old was fouled in the internal seating area, reinserted the plug on the now drained pressure tank, closed the drain line valve, opened the radiator vents and slowly refilled the system bleeding them until the moving pressure needle was at 12. I did not relight the pilots or repower the system. To my surprise, even with the feed water valve turned closed, pressure continued to slowly build and continued to do so with me periodically activating the relief valve to bring it back down.

I got it back down to 11, tightened the supply valve as much as I could (I suspect it is leaking and our village water supply is 48-50). I relit the pilots, repowered the thermostat and pump and brought her up to temp i.e. 70 degrees for the house which is about 140 degrees on the system and pressure has built up to 30 with the new valve doing the weeping routine though greatly reduced about a gallon every 24 hours.

I’m thinking I need to power down, shut off the burners and redrain the system and shut off and drain my water supply system so I or a local plumber can rebuild or replace that water supply shut off valve and also install a local shutoff valve before the heating system, preferably a ball valve.
What are your thoughts and thanks in advance for them? FFF Regards, John

Jamie Hall

Sounds like you've got it. Valves do leak after a while, sometimes...

Intplm.

Yes. Probably the auto-feed is passing water.
If you have a fast feed manual feed/bypass valve feeding the boiler. Check to make sure that the valve is closed properly.
The expansion tank could also be waterlogged.
The relief valve might be damaged due to these occurrences.
Do you have a domestic hot water coil on this boiler? A small pinhole leak could also make this happen.

John B Fowler

Thanks. It is a closed system, no auto feed. I suspect the fill valve is the issue. Fully closed so suspect the seat gasket or the seat itself in the fill valve will be the issue. Tank is clear and I drained it. I replaced the relief valve. I have a separate gas hot water heater.