Boiler pressure gauge inaccurate - now what?

Using NJ Trooper's sticky, I bought a 0-30 PSI gauge and a FGHT adapter and put it on a drain valve. It is showing a variance against the boiler's gauge - the pressure on the boiler was showing at 20psi while the new gauge was reporting closer to 15. What is the next step - should the boiler gauge be replaced? Or is it OK to leave the new gauge on an open drain valve and just use that as the accurate reading?

On a related note, the distance from the boiler to the highest baseboard radiators on the 3rd floor is about 27 ft, so using the formula (height * .433 + 4) I figure the minimum pressure should be around 16psi. Is that what I should shoot for as a cold/off pressure reading?

 

You could replace the gauge if you want... not necessary really as long as you know it's wrong.

You could leave the new gauge on, but me personally would probably close the valve and only open it when I wanted to know the pressure for whatever reason.

Yes.

 

So I thought the new gauge was working but now i'm not so sure. Had the heat running today, with all 5 zones running. The new gauge connected to one of the drain valves for one of the zones shows a constant 15psi. The boiler gauge reads 25psi at 180*. Problem is, the pressure relief valve is slowly leaking out some water. Anything sound off here?

Here are some pictures:
new gauge on drain valve:
http://i.imgur.com/9HfPAUe.jpg

boiler gauge:
http://i.imgur.com/H7zZcQN.jpg

pressure relief valve:
http://i.imgur.com/Y875FIr.jpg

 

additionally, i checked it again this morning after being off for about 10 hours. new gauge showing 12 psi, and the old boiler gauge is showing the same at around 70*.

 

As a Real Estate Broker, I have very limited experience with Pressure Relief Valves; but I've been told that once they pop, you can seldom get them to properly re-seat completely, and you will often experience continued "weeping". Maybe that's what you're experiencing.

So I've found myself always replacing them; considering them to be a consumable device . . . . only there for safety purposes until needed.

Maybe I just haven't developed a good technique for cleaning the seat ?

How do professionals clean the seats of these PRVs, once they've popped ?

 

IF you are sure the water pressure is below 30psi then replace the safety valve .

 

If a relief valve is not 'excercised' regularly they will almost always have to be replaced.

Some ppl (including myself) recommend replacing them as routine maintenance every five years as a matter of course.

One thing that I've tried that works from time to time is to lift the handle fully and let it 'snap' shut.

Some of the difference in the gauges could be due to the location of the gauge relative to the system pump. You could see a difference of 5-10 PSI if one gauge is on the suction side of the pump and the other on the discharge side.

Once the pump stops, the difference between gauges should be nil... at that point only the pressure difference caused by the height ( 0.432 PSI / FT ) should be seen.

 

I haven't heard the theory that once a relief valve lifts, it's likely shot. It is often recommended to manually lift the relief valve for a couple of seconds every few months - that should flush any debris.

It's also recommended to replace the relief valve on a routine basis, maybe every five years. But since your relief valve is behaving suspiciously, go ahead an replace it. You will need to depressurize and cool down the system - in which case, I would go ahead and replace the boiler gauge as well. Having two functioning gauges is nice.

By the way, the gauge you have on a drain valve won't indicate boiler temperature correctly - for that, the gauge needs to stick into the boiler water itself.

 

Most of us have tried lightly tapping the stem of the leaking safety valve with enough success that we will try the next time we find a leaking valve. Since we are required to exercise the valve during annual servicing , the valve may then not seal .

 

I like the way you said that!

There's lots of things that I keep trying with no success... most of the time I end up getting slapped.