Hydronic Loop Was Working then Stopped

MrCofDG

One room of our house with 2 exterior walls has two runs of cast iron BaseRay baseboard (13.5' long and 15’ long); they are connected by a union in a corner. They are supplied via mono-flow tee (Bell&Gossett I believe), from the 1st floor’s main loop (in adjacent crawl space), and there is a supply valve on one end that I have never closed. This room is on a slab, and dates from early 1960s.

Problem: Room heated up nicely from at least 1991 thru ~2009, then baseboards stopped working (stayed cold even though all air was bled out of ‘em and rest of 1st floor heated up) from then until October 2014. In October 2014 a plumber did some work in the basement (non-boiler related), and the baseboards suddenly started heating up again, and ran fine and hot thru May 2019. In summer 2019 I drained much of the water out of the system to repair a circulator pump. When I restarted the boiler system in fall 2019 the baseboards in this room stayed cold; and when I bleed them I get only water – some warmth will start to appear near the supply valve and maybe 5 more feet downstream, but when I stop ‘bleeding’ the water (e.g., after an hour or even 2 hours), the room’s baseboards revert to cold.
I humbly request your suggestions/recommendations.
(one other note – I’ve played around with lowering/raising boiler temperature, and raising/lowering boiler pressure – no luck).

Diagram attached (created in Microsoft Word), and one pic of the corner:

Paul Pollets

Try posting a pic of the boiler and near-boiler piping. If the zone is using it's own pump (or zone valve) check the wiring when calling for heat. When calling for heat, the piping and radiators should be significantly warmer within a minute or 2, bleeding for an hr or more tells me it's probably not an air problem.

pecmsg

Bleed the air form one side at a time.

HVACNUT

Two people.
Crank the heat.
If there's a Lo aquastat, turn it all the way down.
One person start bleeding.
The other keep boiler pressure near 30 psi without blowing the relief valve.
It won't be easy. Long monoflo runs can be a real pain in the butt.

No evidence of a slab leak?

MrCofDG

Thanks all.

Paul, the zone (entire 1st floor) is using its own pump and it works, i.e., entire 1st floor gets heat except the above-mentioned room. I agree it's probably not an air problem.

pecmsg, I have 'bled' both of the rads today (the 15' one and the 13.5' one) and both spewed only water..... is that what you meant?

HVACNUT, I have, a few weeks ago, tried the 2-man bleed approach, while pushing the pressure up to 30 PSI - alas one of the pipe fittings (in basement) started leaking then, so I had to back off. What do mean by "If there's a Lo aquastat, turn it all the way down." ? (My aquastat relay has only a high limit setting.)

pecmsg

MrCofDG said:

pecmsg, I have 'bled' both of the rads today (the 15' one and the 13.5' one) and both spewed only water..... is that what you meant?

Close the supply and blead the radiator. Open the supply and close the return and blead it again.

MrCofDG

I could, theoretically, close the supply valve and bleed the (13.5') rad, but I'm very concerned that the supply valve would start to leak since it has not been used in decades. And, there is no return valve that I know of......

pecmsg

The issue is the water is following the path of lease resistance. If theres an air pocket in one of the lines you wont move it with a bleeder.

HVACNUT

> @pecmsg said:
> (Quote)
> Close the supply and blead the radiator. Open the supply and close the return and blead it again.

Most monoflo systems dont have isolation valves at the boiler. No purge station. Nada.

MrCofDG

As I understand your March 28 post above re "Two people...", I will give that a try (since that last time I raised the pressure to 30, i had the t-stat off). I'll report back. Thanks.

HomerJSmith

No heat, no flow If the boiler is putting out heat, it is as simple as that. Flow is the conveyor belt of heat energy.

The Monoflo system is a two path system. Water flows thru two paths. One path thru the baseboard and one path continues down the line to the next Monoflo tee or the boiler return. The Monoflo tee diverts the water supply to these two paths. Gee, I guess that's why they call the Monoflo tee a diverter tee, hmmm! Who woulda thought.

I'm assuming the baseboard are not air bound, if you can bleed them.

The question is what's causing the no flow condition? One has to know the flow path from the boiler to the boiler return. If you have one circulator and more than one zone and the other zones are getting heat, one can assume that the circulator is working properly. If there is a zone valve on the Monoflo circuit, is it opening and therefore allowing flow? Is the thermostat, wiring to the zone valve, and transformer functioning properly? Is there any valves (ball, globe, gate) in the circuit that may be closed or throttled down?

If the fore going is working properly, I would look for an obstruction in the piping path, itself, because of rust or other debris. The obstruction doesn't have to stop the flow, just obstruct the flow.

If the return to the boiler from the problem circuit is hot, look for an obstruction in the baseboards. Possibly the connection between the two baseboards as shown in your picture.

Your sys looks old and black iron pipe does degrade even in a closed sys. Pics of your boiler, etc, would be helpful.

HVACNUT

@HomerJSmith
Nice post but you didn't start from the beginning.

It's just one radiator with a long run under a slab.

HomerJSmith

I guess my eyes aren't working properly. I thought I saw two baseboards in the picture.

To me it appeared that the baseboards are in a basement with the supply and return coming from overhead? If so, it is possible to vent the baseboards and still have the circuit air bound at the high point in which case the flow required to push air down a vertical pipe would be in excess of 2 feet/sec.

It kinda hard to have a crawl space under a basement slab, so perhaps the Monoflo tees are in the ceiling of the basement under the 1st flr crawl space. If the fore going is true...

Then the baseboard should fill with water thru gravity flo.
When pushing water down to a heat emitter, the requirement is 2 Monoflo tees, one on each end of the heat emitter circuit.

I would want to know if the return pipe from the base boards at the boiler is hot. That would tell me that there is flow, just not thru the baseboards. I don't think a plumber working on an unrelated problem has anything to do with your problem. I would suspect the valve and probably replace it with a fully ported ball valve. If that valve is a gate valve and it is two days older than Moses, the gate may have stripped off the stem and creating a blockage. Look there and make sure the valve is completely open even if you have to remove the bonnet and pull the stem out. Pics can save a lot of guessing.

HomerJSmith

If the supply to the baseboard is a globe valve, then I would suspect that the rubber seal broke and maybe that is inhibiting the flo.

coby

I agree with previous post's Monoflo systems can be a pain to bleed and working properly when issues arise. But if you want to simplify your problem I would add a pump to that zone.

MrCofDG

Just got back today. 1st some clarifications (after reading Homer's comments) - the 2 baseboards are on a slab, and are fed by mono-flo tee in the adjacent crawl space. I will try to get photos of the relevant in-crawl-space connections.
The return pipe from the 1st floor zone is hot (all of 1st floor is hot except the 2 baseboards on the slab) and 1st floor zone circ works just fine (no zone valves). The first floor piping/baseboards is old (late 1950's or early 60's)

Now following up on HVACNUT's above 3/28 comment - my wife & I did that 'operation' yesterday; alas, it didn't help (the 2 rads still cold this AM); here's what we did specifically:
1. Lowered the aquastat's high limit to ~145 degrees.
2. Raised 1st floor t-stat to hold @ 77 degrees.
3. I stayed in basement and kept boiler pressure raised to 26-27 PSI.
4. We "bled" water continuously from far end of the long radiator (had tube running from bleed valve to concrete basement steps) while the circ ran continuously.
5. Did this continuously until both rads were warm (took ~5 hours).
Wrapped up the operation by closing the bleed valve, lowering boiler pressure back to ~20 PSI, returning aquastat to ~185 degrees, and t-stat to regular programming.

I'll get photos as mentioned and post 'em tomorrow. Cheers.

Alan (California Radiant) Forbes

Try adding 1 or 2 tablespoons of Dawn dishwashing soap to your boiler water. It's a release agent for air bubbles.

MrCofDG

Thanks Alan. I'd probably have to pull off relief valve to do that. And thanks coby, adding a new pump/zone for the slab room is on my list of possibilities.

Following up on my above promise of photos - I added 5, taken hunched over like a coal-mine mule in the crawl space . Yes, the A word is relevant . Also, I'm no longer 100% sure diverter (or mono-flo) Tees were used, maybe u experts can identify the type of T's used; but again, the rads on the slab were working from 2014 thru fall 2019.

MrCofDG

Update: I took off the old pressure relief valve, and added 2 Tbsp of Dawn d/w liquid to the boiler, and put on a new PRV. Alas, the baseboards in the problem room (see original March 28 post above) stayed cold. My planned next step, probably in May: add some boiler de-scale liquid to the boiler system, e.g., Hercules brand “OIL FREE BOILER & HEATING SYSTEM CLEANER WITH SILICONE”.

Alan (California Radiant) Forbes

Patience.........these things take time. Keep the pressure at around 20-25psi.

MrCofDG

I'm not sure I follow.... do you mean keep the pressure at 20-25psi during general/normal operation ??

Alan Welch

If your looking for reccomendations,I would say call your local heating professional. If you want a suggestion of what to try yourself I would put a purge setup on the return where it comes back into the main.. If you have poor flow through the radiation the valve you didn't touch could be the problem..

Alan (California Radiant) Forbes

MrCofDG said:

I'm not sure I follow.... do you mean keep the pressure at 20-25psi during general/normal operation ??

Yes, the higher pressure will make the air bubbles smaller and easier to move around.

EdTheHeaterMan

@MrCofDG said: Problem: Room heated up nicely from at least 1991 thru ~2009, then baseboards stopped working (stayed cold even though all air was bled out of ‘em and rest of 1st floor heated up) from then until October 2014. In October 2014 a plumber did some work in the basement (non-boiler related), and the baseboards suddenly started heating up again, and ran fine and hot thru May 2019.

the work the plumber did here that was "non-boiler related" but may have contributed to the resolution. Think about what work was completed... Is there a valve, or a fitting or plug or other plumbing looking item that was inadvertently touched, adjusted, or opened or closed that may have contributed to the assumed unrelated heat resuming?

I am not saying that this is your exact piping condition.. just check out the illustration to see how an airlock may be your problem


The heating system pump is not like a pump that you might use to get water out of your basement. The lift capability of that pump would make your heating system very noisy. A circulator has very little lift capability when compared to other pumps you are familiar with. The weight of the water going up a pipe is offset by the weight of the water going down the pipe. So the pump does not need to be very powerful to circulate the heat.

Also, if there is another path for the water to follow, then it will take the path of least resistance. (the path without the air blockage.) even if it is a longer path... if there is no blockage, there is less resistance.

@DanHolohan used to teach in his seminars that you have to use your mind's eye to see where the water is going to go. You just can't put an arrow on a pipe and hope the water will follow the directions.

Even funnier, He would tell the "engineers" the arrows need to be on the inside of the pipes so the water could see which way it needs to go.