High Pressure in Boiler

Utah

My boiler is producing high pressure and setting off the pressure relief valve. I've purged the air out of the each of the 4 zones, replaced the pressure tank, replaced the pressure relief valve and replaced the auto-feed valve. All parts came from Home Depot if that makes any difference. The pressure gauge appears to read about 20 to 25 psi when up to temperature. Any ideas?

SuperTech

Replace the expansion tank if it is a diaphragm type. Make sure the air pressure in the new tank is 12-15 PSI before you install it. 

If you have an older compression tank strapped to the ceiling in your basement you probably need to drain some water from it and let some air back in the tank.

Jamie Hall

If the pressure relief valve is releasing at 20 to 25 psi or so, either it or the gauge is lying to you. It may need to be replaced.

There are some things I purchase from Home Depot or Lowes. Things like pressure relief valves and expansion tanks are not among them.

Intplm.

@Utah Is the gauge lying to you? It may not be reading correctly. Change it ??

The relief valve should discharge at 30 psi. Your auto feed valve should be factory set at 12-15 psi, and should match the air pressure in your expansion tank.
After you verify that those items are working properly you will notice that the boiler will rise in pressure when the boiler is running and finally shuts off at temp. When that happens lower your pressure to the proper settings and monitor the boiler for a few cycles. You should be all set at that point provided that the things you purchased are working correctly.
I have found that the big box stores do not have much quality control once there stock has been put on the shelf.
I have found boxes with defective items thought to be new with unseen damage right out of the box. Old items returned by another customer. Damaged or used by that customer and then repackaged and put on the shelf. (This has happened to me.)
Be aware that this is also a possibility, but try the before mentioned directions first. After you do that. You should be good to go.
Good luck.

SuperTech

I was thinking that the boiler may be at 25 PSI when up to temperature or at high limit but the relief valve already dumped the excess pressure.  I wouldn't be surprised if the gauges is inaccurate either.  

Usually when the bladder expansion tank is the culprit its can be easily confirmed by tapping on sides and checking if its waterlogged.  

MaxMercy

Utah said:

I've purged the air out of the each of the 4 zones, replaced the pressure tank, replaced the pressure relief valve and replaced the auto-feed valve. ... Any ideas?

The only other thing that comes to mind is whether it has a tankless coil. A small leak in the tankless coil if so equipped will expose the boiler to domestic water pressure. Such a failure adds water directly basically bypassing the pressure regulated auto fill valve.

MaxMercy

Intplm. said:

I have found that the big box stores do not have much quality control once there stock has been put on the shelf.
I have found boxes with defective items thought to be new with unseen damage right out of the box. Old items returned by another customer. Damaged or used by that customer and then repackaged and put on the shelf. (This has happened to me.)

^^ This. ^^

I'm not a pro, but have always dealt with the local plumbing supply houses, mostly because I'm a small business owner and prefer to deal with the same. Unfortunately, far too often I'll need something on nights, weekends, or holidays when my local guy is closed. I swear everything including my cars decide to quit on nights, weekends, and holidays, but I digress.

Just recently, I needed a Taco 3 zone relay on a Saturday afternoon and the local Home Depot had two, both with boxes that were open and then taped closed. This could be some amateur just wanting a look inside, or it could have been installed and found not to be the problem and returned, or it could have been miswired and damaged. Fortunately, there were four other HDs within 30 minutes and I found one with an unopened example.

Big Box Stores of any color will take back anything without question, which is good for the returner but bad for the next buyer. I will not buy any electronic control that's been opened.