Very old boiler, pressure relief releasing water. acceptable reducing pressure?

[Jadnashua]

You have some quite large pipes in that boiler system, and a fairly small expansion tank. That implies a fairly hefty water volume. How did you decide what size tank was needed? There are some on-line calculators you can use but you need to know three things to have a good end result:
- total volume of water in the system
- minimum water temperature
- maximum water temperature

IF the old configuration had some air in it and now you've essentially purged the air, that could make a difference. Water doesn't compress...air does.

 

[Astro46]

he, he. yep. I was happy to come up with that solution for a stable tank cradle. And, it just fits under the admittedly too long space heater (hasn't been used in years) vent.

 

[Sponsor]

 

[Astro46]

You have some quite large pipes in that boiler system, and a fairly small expansion tank. That implies a fairly hefty water volume. How did you decide what size tank was needed? There are some on-line calculators you can use but you need to know three things to have a good end result:
- total volume of water in the system
- minimum water temperature
- maximum water temperature

IF the old configuration had some air in it and now you've essentially purged the air, that could make a difference. Water doesn't compress...air does.

I think that there is little chance I will come up with a reliable number for volume of water in the system. Too many variables.

As I mentioned earlier, I didn't decide about the size of the tank. I went to a Chicago plumbing and heating supply, explained that I needed to replace the existing expansion tank, telling them the size of the existing. They told me that a diaphragm style, which would be much smaller, could replace the existing non diaphragm tank. Since they supply parts for many years for buildings like mine I presumed that they knew what they were talking about. In fact, the previous situation, which had been going on for years under the care of a professional heating company, similar to the problem that I have now, of pressure relief releasing water, stopped happening, after installing the diaphragm tank, and lowering the reducer valve pressure a bit. All was fine for years.n fact,

Which is why this is so frustrating. that it started again. From just replacing a pump bearing!?

 

[Astro46]

btw: I just noticed that there is a tag on top of temp limit switch that indicates minimum temp of 110 (switch closed) and upper limit of 200 (switch opens) or whatever the pointer is set to (currently 165). I don't know if there is a control for the lower limit inside the switch cover.

 

[Jadnashua]

1g=231 cubic inches...an estimate of the length of the lines and their ID, plus you can look up the specs on the radiators and boiler, and you should get close to the total volume of water in your system. A larger ET than required only hurts your pocketbook slightly.

If you've tightened up the system and eliminated leaks, the expansion volume now becomes more critical than it may have been previously.

 

[Astro46]

I know that what you are suggesting makes sense in designing a new system, where everything is exposed, and data is available for all components.

In this case, estimating the length of line and ID is guessing, at best. As I mentioned, its a two flat. pipes running through walls and floors, with no idea of where they change sizes or exactly where they all run. I tried to find info online on the boiler once; nothing. Wouldn't it be easier to measure the size of original expansion tank, and assume that the plumbers that installed the system (and 100's more like it) knew what they were doing? which is how I got the current diaphragm tank. Of course, the salesman may have made a mistake in his recommendation, but it did work for years.

What are you referring to "tightened up the system and eliminated leaks"? there were no leaks.

The original question remains: why was all the same equipment working without problem until oct, when the new circulator pump bearing housing was replaced? Its not like this is newly designed system.

 

[Dana]

If the boiler is actually falling to 110F and rising to 165F 200F that's good for efficiency, but creates a large change in volume. Or is that just the adjustment range on the aquastat?

Drop the temp to 140F. The boiler will cycle on/off more, but it's temperature & volume won't swing as much. Don't bump it any higher than 140F unless it's not keeping the place warm overnight.

 

[Astro46]

If the boiler is actually falling to 110F and rising to 165F 200F that's good for efficiency, but creates a large change in volume. Or is that just the adjustment range on the aquastat?

Drop the temp to 140F. The boiler will cycle on/off more, but it's temperature & volume won't swing as much. Don't bump it any higher than 140F unless it's not keeping the place warm overnight.

110-200 is the min-max for the temperature cutoff switch.
I will try lowering the max boiler temp.

 

[Jadnashua]

Worst case if you don't or can't estimate by the lengths, capacity, and diameters of the components might be to just drain the system and measure how much water comes out. You won't get it all out, but depending on where the drain valve is, you'll probably get most of it.