Dripping even though expansion tank is empty

I recently has some work done on my heating system (valves replaced, radiator turned around, etc.)

After turning the heat back on, water has started dripping from the pressure relief valve when the water heats up.

I drained the expansion tank (a good old-fashioned conventional expansion tank). But I neglected to turn off the inlet valve before doing this.

After draining the expansion tank, water continues to drip from the pressure relief valve when the burner fires for a few minutes.

The valve to the expansion tank is open.

1) Did I screw up by not shutting the inlet valve to the expansion tank before draining it? If so, how can I fix this?

2) Do you think there may be a problem with my pressure valve?

Any help is much appreciated!

 

You left the inlet valve to what open? The inlet valve to the expansion tank? You have to depressurize the exp tank, and then drain it to allow air to fill it. I think all you did was flush the tank with water, not fill it with air.

If your exp tank is set up correctly, it should never lose its air cushion. By any chance, do you have an air removal device that vents air to atmosphere? They should never be installed with a conventional exp tank.

What does your pressure gauge indicate with the system cold and hot?

[and at what temperature cold and temperature hot - NJT]

 

I dunno if 'screw up' is the right word... you didn't HURT anything if that's what you mean.

Do it again. This time, close the valve to the tank.

Be aware that when the water stops flowing from the tank, you will probably still have water IN the tank. Same way a drinking straw holds drink when you put your finger over the end and lift it out of the glass, so will the tank hold the water.

Using a hose that's only long enough to reach the drain or bucket without being looped all over the floor helps.

Keeping the hose fitting at the tank a little loose so it can suck some air helps.

Worst case you may have to blow back into the hose to break the vacuum in the tank. You may have to do this several times, but the tank must be completely empty before you put it back into service.

If you do decide to blow back in, be aware that you have to be quick about it or you will get a face (or mouth) full of nasty stinky boiler water... you don't want that!

If you have a small air compressor, you can use that instead.

 

Hi Mike Speed 30,

I'll get a better cold pressure readings tomorrow, when the heat is off.

The heat has been on already this evening, but the burner had not been fired up for a short while when I checked. Pressure reading was less than 20. As the burner had been on for 30 minutes or so, it slowly got up to 25 or so, and that's when the slow dripping started.

I don't have an air removal device on the expansion tank. I did notice that the pressure release value was hissing during and for a short while after draining the tank.

BTW, should the valve for the water supply from the house into the system be open?

 

Thanks NJ Trooper.

Instead of using a hose, which is what I did. Perhaps simply draining into a big bucket might be better... that way air could get in? It would be a bit more laborious, but at least I wouldn't appear on America's Funniest Home Videos covered in water as I try blowing in the hose :-)

 

Oh darn... you must have spotted me outside the window with my video camera!

Using a bucket will work also, but there's still a good chance of getting a vacuum in the tank... you might still have to somehow 'break' the vacuum. I'll never understand why the old tanks didn't have a valve on them, up HIGH on the tank... Bell & Gossett makes (or used to make) a few 'trick' valves that would work as a vacuum breaker...

Nor should there be one ANYWHERE on the system...

As long as the valve in the line to the tank is closed, it shouldn't matter. Just make sure the boiler is off so it doesn't fire up while you are draining.

Your pressure gauge could be slightly inaccurate, and/or the relief valve is 'tired'. But relief valves really don't last forever... the seals dry up and crack... 'crud' builds up around them, and when the valve is opened the crud gets under the seat, then they rarely seat properly and usually leak... if it's more than 5 years old, replace it as a matter of preventative maintenance.

If the cold pressure is around 15, and the hot pressure is approaching 25, I think properly draining the tank will get that under control.

 

Thanks for all the help. I just thought I'd put my resolution in here for those that may be looking later.

When I was using the hose (which was long and has many loops), the water would stop coming out the hose. I though the tank was drained. It was not.

This time I used a 5 gallon bucket. When going directly from the faucet on the end of the expansion tank into the bucket, the faucet was able to gulp air every few seconds. Using this method, it ended up taking 90 minutes or so to drain the tank.

FYI, after draining the water, I re-opened the valve to the expansion tank. There was a quick rush of water, followed by "hissing" from the pressure reducing valve. With the emptying of the tank, the pressure had gone down to 8. After a minute or two of hissing from the valve, the pressure was back to 14, and all was well.

Again, I'd like to thank the experts on this forum for their help. It is much appreciated!