Burnham boiler servicing?

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Grog66

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I have a Burnham boiler a little over 20 years old with a bladder expansion tank the same age ..The only things that have been replaced is the high vent and auto fill valve which was done about 5 years ago the circular pump pump was replaced about 16 or 17 years ago and high vent in 2019..Issue is the pressure will get to 26 to 27 pounds ( single story house on a crawl space 1300 square ft ) The PRV has never gone off or leaked and as far as I know that it has not been messed with to see if it worked manual or not ..The unit has been serviced once a year to once every other year ..Should I check into this PRV ? I do have a new expansion tank that I might need to replace and need some advice on as well ..
 

Fitter30

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On the opposite end of bladder tank is a plastic cover remove it should like a tire valve. With the boiler cooled down 100* and pumps off the bladder tank can be checked with a tire gauge 0-50 lb and tire pump to add air if needed. Boiler water pressure should be 12 lbs. First check pressure if water comes out tank is bad. Just air fill bladder to guage pressure. If boiler water pressure is still over 20 lbs valve prv off. Drain little water out of it not from relief
 

Grog66

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Thanks fitter30 , Its cold around here now how long do you might think it might take to cool down to 100 degrees ? I have heard 4 to 6 hours ..I also tried the let a bit of air out of the expansion tank which blew air and water mist more air then water , would you consider this a bad tank ? the tap test sounds just like like a normal tank with top have with a dud and bottom sounding empty
 

Dana

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Thanks fitter30 , Its cold around here now how long do you might think it might take to cool down to 100 degrees ? I have heard 4 to 6 hours ..I also tried the let a bit of air out of the expansion tank which blew air and water mist more air then water , would you consider this a bad tank ? the tap test sounds just like like a normal tank with top have with a dud and bottom sounding empty

It's likely that the water mist coming out with the air was condensation, not leakage (or it would slowly have filled the tank no matter what.)

To properly set the air charge in-situ requires that you estimate the target operating pressure, then bleed water out of the system until the system pressure gauge is ~3-4 psi below that pressure, then pump air into the expansion tank until it hit's your target idling pressure. If doing that raises the system pressure, bleed more water and repeat. In only a few cycles pumping the tank to pressure will no longer raise the system pressure. At that point, add water to the system until it hits the idling pressure. Re-check the air pressure to verify that it matches. In rare instances you'll have to bleed a bit of air to lower the pre-charge 1-2 psi to hit it dead-on, but starting out only 1-2 psi high isn't a disaster.
 

Grog66

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Thank you Dana , I believe I might get what you are saying. at this time I have had my auto fill water valve shut off for about a month thinking that it might have been the issue but I truly feel its the expansion tank ..I have shut the unit down and have waited till the temperature has dropped down to 130 degrees.. When i checked the temperature / pressure gauge and the pressure was at around 18 to 20 pounds at that temperature of 130 degrees ..I believe the pressure should be around 12-15 psi at a cold temperature on the boiler of 100 degrees ..Dana would i need to wait for the system to cool down at all ? before doing what you are saying ..The target idling pressure in your opinion would this be 12-15 psi ? Like i was thinking ? Thanks again for the info New to the boiler world ...
 

Dana

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Thank you Dana , I believe I might get what you are saying. at this time I have had my auto fill water valve shut off for about a month thinking that it might have been the issue but I truly feel its the expansion tank ..I have shut the unit down and have waited till the temperature has dropped down to 130 degrees.. When i checked the temperature / pressure gauge and the pressure was at around 18 to 20 pounds at that temperature of 130 degrees ..

I believe the pressure should be around 12-15 psi at a cold temperature on the boiler of 100 degrees ..Dana would i need to wait for the system to cool down at all ? before doing what you are saying ..The target idling pressure in your opinion would this be 12-15 psi ? Like i was thinking ? Thanks again for the info New to the boiler world ...

The target pressure is related to the vertical distance between the system's pressure gauge and the highest radiator on the system, but not to be below 10 psi (when cold). A column of standard temperature water exerts 0.433 psi per foot of depth, so if it's a boiler in the basement with the boiler's gauge 7' below the floor above, and it's a 2 story building with 10' per floor, and the top of the second floor radiator is 3' off the floor you're looking at 7' + 10' + 3' = 20' of elevation difference, so just to get the water to fill to the top of the top floor radiator takes 0.433 x 20' = 8.66 psi, call it 9 psi. It takes that much pressure to lift the water that even when the system is stone cold, no pumps running.

To keep the top of the system pressurized above room air pressure (so that it can't suck air into the system)when the pumps are running, add another 3 psi. So the target pressure when operating would 9psi +3psi= 12 psi. That would be a pretty reasonable target pressure for 95% of all homes out there. But if the vertical distance is greater than 20' it needs to bumped up accordingly. With some high head water-tube boilers or limed up cast iron boilers it might need another 2-3 psi to keep the boiler from experiencing flash-boil sizzle/pop/banging aka "kettling". But for most 1-2 story homes it will never need to be higher than 15 psi.

It's fine to set the system pressure while the system at 130F if that is at or below the normal low-limit operating temp. If it's a cold-start boiler DO note the pressure on a mild low to no heating day, when the boiler drops to <100F, just to be sure that it's still above 10 psi. Below 10 psi almost all cast iron boilers will experience some amount of kettling on a cold start- often with some alarming (but not particularly damaging) clanging & banging. Kettling doesn't damage the equipment, but it does reduce the heat transfer efficiency, and it's annoying as hell to listen to at 5AM when the setback thermostat calls for heat.
 

Grog66

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Thank you very much Dana, nice explanation i will for sure be working on the boiler this weekend.. The temperature might get up to 60 this weekend ..
 
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