replacing pressure relief pipe from cast iron boiler - how bad?

Helpsing

I have a 1990 hydrotherm boiler that is in pretty good shape except for one thing. The pressure relief valve has been leaking for what looks like decades, to the point that the pipe from the boiler proper is very corroded. (there is no drip tube...) I'd like to replace the relief valve, but I'm pretty sure that will be just the start of a cascade like a cheap sweater, and honestly even if it comes off clean I'm not happy about how rusty that pipe is.

I imagine that the other end of it is "simply" threaded into the cast iron heat exchanger with a bit of pipe dope. But I'm not taking for granted that I can "simply" remove and replace a length of 1" iron pipe from 30 year-old cast-iron.

Assuming that once I get eyeballs on the heat exchanger itself, it looks to be in good repair and not visibly corroded, how likely is it that pipe will have completely welded itself to the cast iron? I'm obviously planning to replace this before too long, but if I can stretch it a few more years that would be better.

EBEBRATT-Ed

Take the nipple out with the valve on it. If you can't get a wrench on the nipple because the valve is in the way take the valve off first. Then find something that will fit inside the nipple to keep the nipple from going oval and put a wrench on the nipple and back it out. Don't let whatever you use drop inside the boiler.

Use a big enough wrench at least a 14" or better yet an 18" You can get a cheap one from Harbor Freight


If the nipple breaks cut some slices in it and cut it out with a cape chisel.

STEVEusaPA

You also might need a tap to clean up the threads.

Helpsing

To clarify: I'm sure the expansion tank was waterlogged, probably for years. That's been fixed. This pressure relief rises vertically out of the boiler, not out of the side. There's no nipple outside the cabinet, just 1" iron straight into a PRV. The valve isn't noticeably "dripping", it's just a tiny bit wet inside and probably drips one drop a month. Just enough to rust.

EBEBRATT-Ed

@Helpsing

That's all the more reason that you need to replace the valve.

A small drip can rust the inside of the valve so that it cannot open.

I actually had this happen on a commercial boiler once. And the the pigtail for the pressure control plugged up. Could have been a disaster.