Pressure relief valve dripping

TJin

My boiler has been having an issue with pressure. It can reach 30PSI and cause the relief valve to drip water. 

I replaced relief valve and expansion tank. But every time about 3 days after the replacement, the pressure gradually reached 30PSI again and I see dripping water.

Do you know anything else which may cause this?

Mad Dog_2

Pictures would help. Could be a few things...Bad or misadjusted feeder valve, undersized/underpressurized Expansion tank. Bypass leak...Mad Dog

pecmsg

Did you check the pressure in the expansion tank before installing it?

SuperTech

A leaking tankless hot water coil or indirect water heater coil would be one thing to check. Was the precharge on the expansion tank checked and set properly before it was installed?

hot_rod

water.ogged expansion tank. Push in. The schrader valve for a second. Do you get air or water coming out.

EdTheHeaterMan

This sounds like a new relief valve and tank were installed and 3 days later the pressure climbed to 30 PSI. Well you know the relief valve is working. It is supposed to drip when the pressure gets to 30 PSI.

Your boiler is connected to your house water pressure at least by one way, and maybe two. The first way it is connected to the house pressure is at the fill valve. If that fill valve is a pressure reducing type, then you need to check to see if it stops feeding water at 12 PSI (or whatever static pressure you have it set to). If it does not, try to close the manual valve and see if that helps. If that still does not solve the problem, then the valve is passing the house water pressure to the closed system very slowly. At a rate of about 2-1/2 PSI per day (I used math to figure out that rate 12 PSI from 30 PSI is 8 PSI. 8 PSI over three days is about 2.6666 PSI per day).

If you eliminate that as the problem and you still have a pressure increase, then you need to look at the Domestic Hot Water (DHW) system. Is it part of your heating system? I mean do you get both heat and hot water from the same burner? If you answer yes to that, then you need to determine if you have a tankless coil that is inside the boiler, or if you have what is known as an Indirect water heater. That is a tank that is connected by 2 pipes to the hot and cold water pipes (the open system) and 2 pipes connected to the heating system, like it is a separate zone on your boiler with a separate thermostat (that is located inside the tank). Either of those water heaters have a heat exchanger that separates the higher house water pressure from the open system, from getting to the lower (12 PSI) closed system.

If that heat exchanger has a small pinhole in it, then there is where you are getting the higher pressure to over pressure your heating boiler to 30 PSI. To test that out just close the cold water inlet to the water heater and see if the pressure stays where it is supposed to be. (You may need to take a cold shower for a day or two during this test.)

I hope this is helpful in getting your problem solved.