Hot water baseboards not circulating water

genericnj · March 2021

Hi all - I have a 1980s gas fired hot water baseboard system with two zones (upstairs and downstairs) located in NJ with a Burnham boiler built in 1981. There was no problems with it to date. Then this morning i was woken up by loud gurgling / water/air chugging sounds from the pipes. I turned both thermostats off and sound went away. Turned the system on again and set temp to 80 to test, I can hear a click at the boiler and a low buzz afterwards (which happened before too), however I am not hearing any water circulating to either upstairs or downstairs baseboard and both baseboards are cold to touch even when both thermos are set to 80. After a few minutes the gurgling sound seems to return until I turn thermos off. I believe there is a single circulator pump with two electronic valves for each zone. I would normally hear a hum when the water is cirucating, especially for upstairs, but i do not hear the hum at all on either zone now. The burner does not seem to fire on either (the water may still be hot from last time it worked).

Troubleshooting I have done:
1. Turned on the water feed to see if the water was low for some reason, i do not hear it refilling any water.
2. Tried flipping the emergency off switch on and off, i can hear a click when i flip the switch, but no other effect.
3. Tried turning on and off thermos on both zones, same effect for either zone.
4. Felt pipe feeding water, feels warm near the circulator pump, but gets progressively cooler up the pipe and after the zone valves.
5. Tried turning the valves for each zone while the gurgling sound happens, I hear a slightly different volume in the gurgling, but does not make the water circulate.
6. Tried tapping the circulating pump with a hammer gently, no effect.
7. Checked pilot on, it is on.

We had a power outage for a couple hours yesterday, not sure if at all related...

Any advice or troubleshooting pointers very welcome. Thank you!

genericnj · March 2021

Quick update - the gurgling sound coming from the pump area is no longer happening (water is not circulating still) - could be that the water in the boiler has cooled off a bit by now since it has been a couple of hours since this started. I still am not hearing the pump circulating as I would in the past and all baseboards totally cold..

genericnj · March 2021

Update #2 - the burner just went on and stayed on for about 1 minute, then shut off - what i believe is happening is the water cooled down so boiler turned on burner, it reheated quickly since it is not circulating and shut off again. Both zones are completely cold and no sound of circulating pump.

EdTheHeaterMan · March 2021

Just so we are clear, the hum is usually because it forgot the words.

EdTheHeaterMan · March 2021

Now to be serious @genericnj

My first thought is your expansion tank (if it is the bladder type) just failed and the air from the tank is now in the loop(s) causing the water circulation problem. When you heard the gurgling the first time, is probably when the failure happened. See if the expansion tank feels heavy. If it is supported only by the threaded connection, a slight push will indicate if it is mostly full of water or mostly full of air.

If you don't have that type of tank and you have the large steel compression tank strapped between the floor joists near the boiler, then there is a different problem.

That is my first impression and where I would look first.

Mr.ED

genericnj · March 2021

Thx for the suggestion, there is indeed an expansion tank close to the circulation pump. I snapped a pic and attached. How would I check if it is heavy though, it is solidly attached to a thick pipe that doesnt have much movement.

Another thing I noticed is the gurgling happens only after the boiler flames run and heat the water and the system is in ON but not circulating for a few minutes, then the gurgling comes back until the water gets cool after the flames have been off for a while, at which point there is no gurgling until the water is reheated again. The gurgling immediately stops when system is turned to off.

HVACNUT · March 2021

Is the circulator hot to the touch? Be careful.

genericnj · March 2021

HVACNUT - the pump itself is very hot - i used a temp probe, it is 200F, however up the return pipe feeding into it the temp drops drastically, 130F just a few inches up and 80F about head-height. Also I checked the temp of the outlet from the boiler, it is around 175F at the exit from boiler, then 135F when it enters expansion tank, then right after expansion tank it is down to 85F and return is around 81F - ambient is 75F and this is after leaving the boiler running for about 30 mins, during this time the boiler fired for 2 minutes, shut off the burners and stayed on with just slight buzz but no low whine like the circulator pump normally makes on this system.

Side note, i checked the gauge on the boiler, but it seems to be shot, it reads 70F and 10PSI without any change even right after firing when the pipes around the gauge read 175F with laser probe.

genericnj · March 2021

Attaching a pic of the temperatures the laser probe shows since the text may be a bit confusing.
Also, the boiler is no longer making any gurgling sounds, even when the burner has been on and off.

genericnj · March 2021

What is that red flow control valve? it seems that the temp drops drastically just past that valve, it is 120F at the input pipe and 85F right at the output of that valve...

HomerJSmith · March 2021

You can rotate that lever on the top of the red valve and that should open it and check the temps again. Pics of the pump and the boiler from further away would be helpful.
The fact that the red valve isn't opening indicates to me that the pump isn't putting enough pressure to the red valve to raise the weight. But, if you have air in the baseboards, the pump will not circulate the water thru the sys. (air lock) That's a flo check valve that allows water to flow in one direction only.

Do you have coin vents on the baseboards that you could open and let any trapped air escape?

I can't see the pump very well, but it looks to be a Taco pump in which the cartridge may be plugged and not rotating. If that is the case I would replace it with a Grundfos UPS15-58FC, 3-Speed Circulator Pump, 1/25 HP, 115 volt.

Is there any dripping from the boiler pressure relief valve? I can't see the date on the expansion tank, but if it is old, it may have lost its air charge. On the bottom of the E-tank is a blue cap that you can unscrew and under that cap is a tire valve. Quickly depress the tire valve stem and see if water comes out. If it does you probably need to replace the E-tank. If this is the original E-tank, replace it.

The E-tank should be mounted about 15" before the intake of the boiler pump for best performance. You are currently pumping into the E-tank where it is now mounted. That is considered a no, no. The air scoop is in the right place tho.

There is a manual lever that allows you to open those two zone valves, but they are probably working if you hear noise from the baseboards.

genericnj · March 2021

I tried rotatign the lever on top of the red valve, it does not budge by hand, I can try a wrench but wanted to confirm it's safe to do so since it is not budging at all by hand.

Do baseboards over time get air in them? I thought it was a fully sealed system and I have not touched it at all in terms of bleeding or draining or refilling.

There is no dripping from the pressure relief valve that i could see at least, there is some rust and debris so at some point some water probably did come out of there, but nothing looks new.

In terms of the pump, sorry but am new to water heating - is the pump the box at the outlet of the boiler (marked as A: in the attached pic) or is it the box on the left (in attached pic marked as B:) at the return? i thought it was the box at the return and the one at the outlet of boiler was a low water cut off, but i could be wrong.

Also attaching a pic further away for better visibility.

I do not hear any noise from the baseboards - only a slight buzzing at the boiler and the boiler firing and shutting off, but no pump whine and no crackling / pump whine at the baseboards.

thank you!

Whole system:

Closeup of pump area:

HomerJSmith · March 2021

"B" is the pump and "A" is the aquastat that turns the boiler on and off and also turns the pump "B" on and off. The Zone Valves are wired to the aquastat and the zone valve's end switch activates the aquastat. The thermostats activates the zone valves. The temperature in the room activates the thermostats. The zone valves have two functions: one, they turn on the boiler thru the aquastat; two, they allow the heated water from the boiler to flow to the baseboard.

The round thingy next to "A" the aquastat is a temp & pressure gauge called a Tridicator.

If the pump is getting 200 deg and the output temp is 135 deg, it leads me to think that the pump is not rotating and there is a lot of heat built up in it. That could be because the (1)cartridge is plugged or something is preventing it from rotating or (2) the aquastat relay is not turning the pump on. If I were to venture a guess, I would think it is the relay in the aquastat. It is not uncommon in my experience to have the solder joint on the back of the aquastat board to break from the vibration of the relay opening and closing and since it is a 2 pole relay, (one pole turning on the boiler and one pole turning on the pump), the pump pole always seems the one that fails.

Of course, the pump should be considered highly suspicious, too. If it is the pump and you have to drain the sys to replace it, I would without question replace the E-tank and the Pressure Relief Valve on the boiler. I would replace the air vent on top of the air scoop, too. All these things are relatively cheap. I can make recommendations for these.

I was looking for your boiler cold water fill valve, an Extrol tank requires one. The last four numbers on the serial # of the E-tank are the month and year of manufacture. Eg. 01(January) 05 (2005).

bucksnort · March 2021

How would you even go about replacing a pump or aquastat on that?

HVACNUT · March 2021

bucksnort said:

How would you even go about replacing a pump or aquastat on that?

Someone decided to box in the boiler. I wouldn't service it unless the wall was opened.
Its either air bound or a bad circulator.

genericnj · March 2021

HomerJSmith - thank you for the detailed explanation, it makes a lot of sense now to me. I really appreciate the time you took to explain the working details.

In terms of the location - yes it is extremely difficult to get to ... unfortunately the house has no basement, so utilities are in a closet in the living room - literally... the wall on the side that would have to be opened is right in center of living room.. I can't even see the gauge without sticking my arm in an awkward way and taking a picture of it backwards....

SuperTech · March 2021

Replacing the circulator wouldn't be too bad, it would be easy enough to get out.

The aquastat wouldn't be too hard to replace either. I would remove it from well then change the wires from the old one to the new one before mounting it on the boiler.

Now troubleshooting the aquastat is a whole different story. It would not be fun trying to get in there with a multimeter and check everything with the location of the aquastat. Fortunately it looks like checking for 120 volts at the circulator wouldn't be as difficult.

Hot water baseboards not circulating water

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