Natural gas fired hydronic boiler question

[brianl703]

This boiler dates back to 1965 (it doesn't leak). This is installed in a house, I believe it's a 100,000 BTU unit.

The question I have is about how the circulator pump is controlled.

It seems that some have an aquastat, and some have the circulator pump turn on when the room thermostat calls for heat.

I fired this boiler up today, let it run for about 10 minutes. The radiators upstairs started getting hot but the circulator pump never turned on.

If the aquastat is broken, what is the disadvantage of wiring the circulator pump to come on when the thermostat calls for heat as opposed to replacing the aquastat? I read that some systems are wired to have the circulator come on as soon as the thermostat calls for heat, and in fact this is how I expected this one to work.

Is the aquastat normally switching 24V to a relay or 120V directly to the pump? (Without removing the control I can't see how it's wired).

I have no idea of the history of this boiler other than that the house it's in was poorly maintained (foreclosure). The air intakes on the boiler for the firebox were clogged with lint from the dryer! As a result the firebox is filled with carbon/soot. I vacuumed it all out.

The gas valve was replaced at some point in the last 15 years or so (it has a part number that was printed with some sort of dot-matrix printer on it).

The temp/pressure gauges seem to be stuck, they're not moving. I expect they need to be replaced.

Where can I get replacement aquastats and gauges and all of the other stuff that goes into a boiler? I have no problem finding parts for gas furnaces but finding parts for gas boilers is proving difficult.

 

[Fester]

I would call a pro, a boiler in disrepair is not to be taken lightly, safety's could be could be frozen like the pressure gages.
The end result could be an explosion.

These things could be wired so many ways, I usually see the tstat wired to a zone valve that then feeds the radiator, the aqua stat would maintain a constant boiler temperature.

Some old radiator systems without water zone valves, would have the tstat turn on the boiler on a call, the boiler comes on the aqua stat just prevents over heating the water, one tstat does the whole house while using multiple radiators, a terrible setup overheats some rooms till the thermostat satisfies.

 

[brianl703]

It is on the short list of things to do to test and replace (if necessary) the TPR valve.

There are no zone valves. The tstat is wired to the gas valve (with an aquastat in series to break the circuit if boiler overheats).

 

[Gary Allan]

All the setups I've seen have any thermostat turn on the boiler and the zone circulation pump. The only difference (that I noticed) was that the boiler local setpoint determined the cutout temp for the burner.

 

[JHZR2]

My boiler is roughly 25 years old, and does not have a zonal system. WHen he thermostat calls for heat, the furnace fires, and heat comes out. The circulator pump never turns on. Your system sounds just like mine...

That is one of the reasons why Im considering replacement... am I better off with a 25yo furnace and a new circulator, or a new furnace with a new circulator... particularly with NG at 10/million.

So, mine does the same thing, only its in a slightly better state of repair. The lack of the pump turning on does not seem to really effect too much, unless I just dont realize it...

JMH

 

[brianl703]

I looked at the boiler again today and it appears that the contactor/relay for the circulator pump is broken. I wired the pump directly to 120V and it works, so the relay is definitely the culprit.

 

[Gary Allan]

My only thought is that without the circulation pump ..and relying on natural convection ..that you would probably overshoot your setpoint on the thermostat. I think forced circulation would be more responsive. I imagine in a cold continuum it would be alright, but it may be less efficient in varying warm/cold day/nights. Probably not as bad as steam.

 

[brianl703]

I'm going to try to track down a replacement relay. I think I could use a fan relay from a forced-air gas furnace, if I can't get an exact replacement. Could also use a contactor from an AC unit. That'd be way overkill for the current the pump actually draws.

 

[brianl703]

An update:

I got a 24V relay from a local supply house. My friend (who actually owns the house with this boiler in it) wired that up and now the circulator pump comes on when the thermostat calls for heat. (Incidentally, the control is a Honeywell Aquastat Relay)

There were gurgling noises when it was running so obviously there was still air in the system.

I also tested the TPR valve. A bunch of discolored water came out, but there was very little flow after the initial burst of water.

It seemed like either the pressure regulator (auto-fill valve) is clogged or the valve to it is frozen, so the system wasn't getting any water supply from the cold water line. I also found that the pressure regulator should have a bypass lever on it which isn't there. This should allow you to bypass it to apply full city water pressure to the system, for filling it quickly and also to test the TPR valve.

Since I'd connected a hose to the drain valve, my friend had the brilliant idea of connecting it to the washing machine's hot water hose to fill the system with water to see if we could get the air out of the system.

It worked! No more gurgling noises, it's silent now. That also tested the TPR valve--it definitely works.

Now the tridicator gauge reads pressure when it's running. Apparently the reason the tridicator gauge wasn't reading anything is that there wasn't enough water in the system.

He'll have to either replace the water valve that feeds the 12PSI pressure regulator or replace the pressure regulator valve itself, whichever is the problem. It looks like the water valve's stem is slightly bent and it won't turn more than 1/4 turn--I know it's not a ball valve, so it's probably frozen shut.

I also used the aim-a-flame to check the venting. The flame didn't get blown out, so it appears to be drafting correctly.

I read on Bell and Gossett's website that they recommend leaving the valve to the pressure regulator closed. Their rationale is that a leak in the system could cause severe water damage.

 

[Gillsy]

If you ever have to replace a bad B&G pump, I would toss it for a Grundfos. They are compact, low in cost, use less energy, and are absolutely silent. Wonderful pump!!!!!!!!

 

[Gary Allan]

Originally Posted By: Gillsy
If you ever have to replace a bad B&G pump, I would toss it for a Grundfos. They are compact, low in cost, use less energy, and are absolutely silent. Wonderful pump!!!!!!!!



We used Grundfos ..they were vertical ..hmm..multistage ..heck, inside it looked like a bunch of vane'd ashtrays that interlocked. The seal was the only complicated part. You had to lift the 25hp motor up to service it. Much larger than what you're referring to, of course.

 

[brianl703]

Originally Posted By: Gillsy
If you ever have to replace a bad B&G pump, I would toss it for a Grundfos. They are compact, low in cost, use less energy, and are absolutely silent. Wonderful pump!!!!!!!!


I think it has a TACO pump. It looks like it's been replaced sometime in the last 43 years.