Burnham gas hydronic system running at 25 psi....

wcweaver3

I recently purchased a 2,300 square foot, 2 story home built in 1940. It has a Burnham natural gas fired hot water system, Model 207NSL-TEI2 (Series 2, Model "B"). It is rated at 198,000 BTU and was built in September, 2000. The boiler serves 2 zones. Each zone has a mix of the old type 1940's radiators as well as baseboard radiators for areas that have been renovated over the years. Zone 2 serves the basement, the first floor and second floor. The circulator pump is a B&G, 1/6 horsepower "series HV, F91, model 102210."

During the inspection period prior to purchasing the house, it was noted that both the pressure relief valve and the temp/pressure gauge were corroded and leaking. Both were replaced and everything seemed to be working ok.

After purchase and during the first cold evening, I fired up the unit and after a short while, the pressure relief valve opened up and dumped water all over the floor. The home warranty people sent out the first contractor who indicated the expansion tank was water logged and needed to be replaced. That was done. Shortly thereafter, the relief valve opened up again and the circulator pump started clattering so loudly, you could hear it all over the house.

The same contractor came out and replaced the circulator pump. About a week later, the clattering started again and the contractor replaced the clutch and that seemed to settle it down. During this entire time, one room on the first floor with baseboard radiators (served by Zone 2) would not warm up - they were cold. A second contractor came out and tried to purge the system (opened up valves, connected hoses to spigots and such) but was unsuccessful. He said I needed new baseboard radiators in that room at a cost of $.

I called the first contractor to see if they had a solution. They came out and looked around and noticed 2 copper pipes that had been capped off in the ceiling and said those pipes serve the room with the cold radiators. Therefore, a vacuum was being created so that's why the radiators were cold and those pipes would have to be re-connected.

In desperation, I reached out to the original owner who told me that he lived there for 7 years, never disconnected any pipes and the cold radiators were due to air in the system as Zone 2 was notorious for air lock up. I finally called a third contractor who told me that most people don't know how to drain these systems properly and he spent about an hour and half draining and purging Zone 2. When it was all done, the cold radiators warmed up nicely. So, here's the problem. Everything seems to be working fine and the cold water pressure (after not firing up all night long) is at 12. However, when the system is operating, the pressure increases to 25 and just hangs there until the thermostats no longer call for heat. The third contractor says this..."you know, that new expansion tank should really be 10 feet away from the circulator pump, not 6 inches. And, you need to check the pressure in that tank and it's so close to the floor (see picture) you can't really get a gauge in there to check the pressure. "

Three questions:
1) Do you think the expansion tank is misplaced and if repositioned would solve the issue? (cost to reposition it and drain/refill system is $)
2) The current water temperature is set for 180 degrees. If I backed it off 10 degrees to 170 would that help solve the pressure problem (i.e. - a lower temperature = less expansion of water = less pressure) but open me up to other issues like condensation and corrosion?
3) Any other thoughts and comments are most welcome!
Many thanks!

hot_rod

Did they check the fill valve to be sure it is not allowing pressure to increase.
Pre-charge on the tank needed to be adjusted.
25 psi is ok if it stays there.
If the expansion tank was connected on the inlet side of that red circulator, I'll be your air problems would disappear.
here is a graphic that shows and explains the importance of the expansion tank connection point.

wcweaver3

Hi - thank you for the graphic! Fill valve was checked and appears to be operating correctly.

Ironman

I'm not sure what you mean by "1940 radiators", but if you have old standing cas iron rad's, that expansion tank may be a little too small.

I totally agree with hot_rod that if you move the expansion tank connection to the inlet side of the pump, your air (and maybe pressure) problems will cease.

Also, what that clueless one said about the tank having to be 10' away, was a load of horse cookies.

Alan (California Radiant) Forbes

With the expansion tank on the discharge side of the pump, the pump cannot add any of the differential pressure it creates to the outlet, so it has to reduce the pressure at the inlet; almost 5 pounds.

When the pump turns on, it will reduce the fill pressure to 7 psi and the fill valve will open and add water to bring it back to 12 psi. When the pump turns off, the 5 pounds is added back in to bring the static pressure to 17 psi. Seventeen psi is actually a fine pressure, but I'm thinking that if this happens repeatedly, it's raising the pressure even more to the 25 psi you see.

Moving the expansion tank to the suction side of the pump should cure your problem.



BTW, I think your boiler is oversized unless you live in a glass house.
It must short cycle like crazy.

Ironman

Also, you could have replaced that expensive energy hog series 100 pump with a wet rotor for about 1/4 of the cost and been better off. That pump that you have is 1950s technology.

A Grundfos ups15-58 or Taco 007 is all you should need.

wcweaver3

Hi - thanks for the great commentary! Yes, by 1940's radiators, I mean the old stand up cast iron ones. I didn't know anything about circulator pumps and a B&G was on there previously, so when the home warranty company said they would replace it, for free, with the same pump, I just said "OK, free is for me!" Agreed that a Taco or Grundfos would be a better choice. When I first read the details of this unit and it said 198,000 BTU, I thought - "holy cow, this is a lot!" When the house was built in 1940, it didn't have much insulation and probably didn't when this unit was installed, but insulation was blown in a few years ago and as far as I can tell, the unit doesn't appear to cycle a lot. And, maybe the Brunham sales person made a bigger commission for selling a larger unit. Many thanks for pointing me in the right direction - really appreciate it!!

bburd

Those cast-iron radiators, and all the water inside them, act like a thermal flywheel to prevent your boiler from short cycling. Count yourself lucky.