Any boiler experts out there?

[LaforzaLand]

I am trying to understand what is wrong with my boiler system as heat is not circulating through the system. This has professionals in my area stumped (which I can't believe). I am in Chicago and the temps outside have been in the single-digits for a few weeks now.

I have an older American Standard boiler with a B/G 1/12 HP pump. The boiler is located in the basement of my home. 3/4" copper piping has been run from the basement (underground) to an external de-attached garage. In the garage there is a supply manifold that feeds the copper tubing in the concrete slab and a return manifold that sends the "water" back to the boiler.

Here's what I know...

1. The boiler appears to functioning as expected to produce heat. The pressure/temp combo gauge on the side of the boiler reads 210 degrees (approx). When that temp goes down, the boiler turns on until the temp reaches 210 again and then the boiler cycles off.

2. The pressure shown on pressure/temp combo gauge on the side of the boiler reaches 10-11 only when the boiler is running and then slowly returns back to zero after the boiler cycles off.

3. The copper pipes within 1 foot of the boiler are always very warm. However, the supply pipe feeding the garage is luke-warm unless the boiler is running. When the boiler is running, the supply pipe is very hot... too hot to touch. That pipe cools down after the boiler cycles off.

4. The B/G 1/12 HP motor and coupler were professionally replaced a few days ago. The motor runs at all times and NEVER turns off unless I physically turn off the power to the motor. The old-school mercury dial thermostat in the garage is set to the lowest setting.

5. The supply manifold (in the garage) never gets warm or hot, and obviously neither does the return manifold.

6. I crack open the valve that is (12") above each manifold, and do not hear any air escaping nor is there any water that comes out of the valves.

Question 1: If the pump motor is running at all times and the impeller is continually spinning, wouldn't the system pressure (on the boiler gauge) be at level higher than zero? Or, is that gauge only for the boiler itself and not the closed loop system?

Question 2: If the supply copper just happens to be frozen between the house and garage, wouldn't that cause an increase in system pressure and cause the circulation pump motor to shut off (pressure safety switch)?

I am looking for guidance to help me better understand why the distribution manifolds are not receiving heated water. Any help would be very much appreciated. Thanks in advance!

 

[NY_Rob]

Almost sounds like either the supply or return pipe in the garage loop is frozen and blocking flow?

You have one boiler that heats your house and garage? You should never see 0 PSI on the boiler pressure gauge, it should generally be in the 12-15PSI range regardless if the boiler is running or off.

 

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[LaforzaLand]

Almost sounds like either the supply or return pipe in the garage loop is frozen and blocking flow?

You have one boiler that heats your house and garage? You should never see 0 PSI on the boiler pressure gauge, it should generally be in the 12-15PSI range regardless if the boiler is running or off.

I agree about the "frozen" blockage in the supply or return line since heat is not reaching the garage manifolds. I wist that I had installed a separate pressures gauge in the system outside of the one on the boiler. I thought that zero pressure is not a good thing. If there was a leak, I should be seeing water somewhere.

The boiler is a separate heating system for the garage. The house has it;s own independent forced-air system. The two systems are in no way connected.

 

[NY_Rob]

^ Well, the good news is eventually it will thaw out.

If it's frozen before, can you use glycol in that system?

 

[Jadnashua]

How deep are the lines to/from the garage?

INsulating them doesn't prevent them from freezing. With the latest cold weather, things could freeze many feet below ground. Because you might consider turning the system off, and that they could freeze along the way or even in the garage, freezing must be considered. If they have frozen, they've probably split. While frozen, they won't leak, but will as soon as they thaw out. Most boilers won't turn on if the pressure is too low, and zero, definitely is! You might want to check the system low-pressure sensor. If the pipes have frozen in the slab, it may be a total loss, and it may also damage the slab. Do you see any cracks in a grid where the pipes may run?

When things have the possibility of freezing, two things are required:
- antifreeze (usually a glycol solution - make sure it is compatible with your boiler and the proper concentration)
- a backflow preventer that will ensure that glycol cannot get into your potable water system from the boiler filler.

 

[LaforzaLand]

How deep are the lines to/from the garage?

INsulating them doesn't prevent them from freezing. With the latest cold weather, things could freeze many feet below ground. Because you might consider turning the system off, and that they could freeze along the way or even in the garage, freezing must be considered. If they have frozen, they've probably split. While frozen, they won't leak, but will as soon as they thaw out. Most boilers won't turn on if the pressure is too low, and zero, definitely is! You might want to check the system low-pressure sensor. If the pipes have frozen in the slab, it may be a total loss, and it may also damage the slab. Do you see any cracks in a grid where the pipes may run?

When things have the possibility of freezing, two things are required:
- antifreeze (usually a glycol solution - make sure it is compatible with your boiler and the proper concentration)
- a backflow preventer that will ensure that glycol cannot get into your potable water system from the boiler filler.

Jim,

Thanks!

The 3/4" copper supply lines are buried 4' below ground in a 4" PVC pipe. They do go up to the surface out in the garage where I suspect freezing would take place. The PVC pipe has a slight pitch so that if the copper supply lines would ever leak, there would be water trickling back into the basement. I do not see any water at the opening in the basement. We'll see what happens in a day or so after the temps outside go above freezing. There is also no evidence that there is any damage or water present throughout the garage floor slab.

I'll check the low-pressure sensor.

My goal, after getting the system operational is to flush the system and replace the 100% water with a glycol solution. The back-flow preventer is a great idea! I don't want to be drinking that anti-freeze stuff.

The one thing that I really don't understand is if the pump is continually running, wouldn't the system pressure be higher if there was a (ice) blockage? And if this is the case, isn't there a "high pressure" switch that would shut down the pump to effectively stop the increase of additional pressure?

 

[Jadnashua]

Most of the circulator pumps cannot build much pressure. They're not like a pump you'd put in a well. They don't normally need to. The outgoing water runs in a loop, so helps. The pump just needs to overcome inertia and backpressure in the lines, and that is not designed to be all that much. Anything that goes out, is getting returned, essentially at the same pressure. They aren't designed to raise the pressure much at all, and, if it weren't for the water coming back, might only be able to push the water up maybe 10' or so. That's one reason why an air lock can stop the flow...there's no water 'falling' back down to keep things moving.

 

[LaforzaLand]

I suspect that there is a mild leak in the system that is preventing the circulation of liquid. It appears that the make up water also doesn't appear to be working or the system would not have air pockets. I'm still working on this one. Thanks to all who have contributed so far.

 

[Dana]

The ice blockage theory is reasonable, but the zero pressure at the boiler at idle is NOT! The pressure needs to be raised to at least 12-15 psi at idle by adding water, but only after charging the expansion tank to 15psi to accomodate the expansion of the system water as the temperature rises. With a properly charged properly sized expansion tank there may be as much as a 10 psi change from the boiler's low-limit temperature to it's high limit.

When a system drops to zero pressure in the basement, the system is then at negative pressure at higher elevations, and prone to taking in air. Air in the pipes can also block flow. If you can't get either air or water out of the zone when attempting to purge air indicates a blockage.

Running a big pump 24/7 even when not needed is an expensive proposition, but would keep the pipes from freezing (if they weren't already plugged). Setting it up to run on a duty-cycle of even 5 minutes per hour even when there isn't a call for heat would be enough.

Under normal operation the circulation pumps only generate a ~2-5psi pressure difference from in-to-out. The system pressure is set by the amount of water in the system.

Running a low system pressure can cause cavitation on the pump impellers, shortening it's lifecycle. It can also lead to "kettling" where the micro-boil in the water contacting the heat exchanger plates inside the boiler become macroscopic, and collapse as the water moves beyond the heat exchanger plates with a sizzle or even banging. This is usually more noticeable at the beginning of a burn than later, and at 10psi it won't be happening at all. If your boiler doesn't have these symptoms on startup when the pressure gauge is reading 0 psi it could be that the pressure gauge is woefully out of calibration (rare, but it happens), and the system pressure near the boiler (at a purge valve or something should be verified with different gauge. Inexpensive pressure gauges such as Rain Bird P2A or PG25-WTG200MP with hose-connection type threads for checking house water pressures that are good enough for a quick sanity check. The markings on those are pretty coars at 5 psi per tick, but the pressure when the boiler is at it's coolest part of the cycle should be between the 10 psi & 15psi marks, and no more than 25 psi at 210F.

Almost no system needs to run a high limit of 210F, and running the system that hot delivers much higher distribution and idling losses. Setting the low-limit to 135F (if gas) and 140F (if oil), with a high differential between the high & low limit is pretty safe from a flue-condensation point of view, and is substantially more efficient.

 

[LaforzaLand]

The ice blockage theory is reasonable, but the zero pressure at the boiler at idle is NOT! The pressure needs to be raised to at least 12-15 psi at idle by adding water, but only after charging the expansion tank to 15psi to accomodate the expansion of the system water as the temperature rises. With a properly charged properly sized expansion tank there may be as much as a 10 psi change from the boiler's low-limit temperature to it's high limit.

When a system drops to zero pressure in the basement, the system is then at negative pressure at higher elevations, and prone to taking in air. Air in the pipes can also block flow. If you can't get either air or water out of the zone when attempting to purge air indicates a blockage.

Running a big pump 24/7 even when not needed is an expensive proposition, but would keep the pipes from freezing (if they weren't already plugged). Setting it up to run on a duty-cycle of even 5 minutes per hour even when there isn't a call for heat would be enough.

Under normal operation the circulation pumps only generate a ~2-5psi pressure difference from in-to-out. The system pressure is set by the amount of water in the system.

Running a low system pressure can cause cavitation on the pump impellers, shortening it's lifecycle. It can also lead to "kettling" where the micro-boil in the water contacting the heat exchanger plates inside the boiler become macroscopic, and collapse as the water moves beyond the heat exchanger plates with a sizzle or even banging. This is usually more noticeable at the beginning of a burn than later, and at 10psi it won't be happening at all. If your boiler doesn't have these symptoms on startup when the pressure gauge is reading 0 psi it could be that the pressure gauge is woefully out of calibration (rare, but it happens), and the system pressure near the boiler (at a purge valve or something should be verified with different gauge. Inexpensive pressure gauges such as Rain Bird P2A or PG25-WTG200MP with hose-connection type threads for checking house water pressures that are good enough for a quick sanity check. The markings on those are pretty coars at 5 psi per tick, but the pressure when the boiler is at it's coolest part of the cycle should be between the 10 psi & 15psi marks, and no more than 25 psi at 210F.

Almost no system needs to run a high limit of 210F, and running the system that hot delivers much higher distribution and idling losses. Setting the low-limit to 135F (if gas) and 140F (if oil), with a high differential between the high & low limit is pretty safe from a flue-condensation point of view, and is substantially more efficient.

Dana,

This is the information that I was looking for. I kept insisting that the system was lacking water but was told that it was only ice blockage by the pros who came out to service the system. That you for the clarification and for the information in operating pressure differences and cavitation issues.

I sincerely appreciate the time you have takent to reply to my posting.

 

[Dana]

You may still have ice blockage, but you SERIOUSLY need to either find competent help, or become your own system-expert.

It's likely that your boiler was installed during the Nixon administration and earlier, and is also likely to be 3x oversized for the actual heat load. Many boilers were intentionally oversized to be able to deliver dometic hot water reasonably with an embedded water heating coil, others don't even have that excuse, and are even ridiculously oversized for the radiation they're hooked up to (meaning, the radiation can't emit the full boiler output into the rooms, which forces the boiler into excessive cycling, taking a toll on efficiency.)

Once you get it back to running in a semi-normal fashion, take the time to run fuel-use heat load calculations on some wintertime fuel bills (is it gas or oil?), to see just how bad the oversizing factor is. Also take the time to measure up the radiation zone by zone to see if your house is a good candidate for a condensing boiler (some are pretty straighforward, some not so much.) Whatever the name-plate efficiency is on the boiler, if it's 3x oversized 50 years old, and has been operated at a high-limit of 210F the odds are the as-used AFUE is under 60%, and a right sized gas fired modulating condensing boiler could cut your fuel use by nearly half, and be more comfortable to boot. If it's an oil burner installing something right-sized for the space heating load can also deliver pretty dramatic fuel economy.

If your boiler room is in an uninsulated basement and is the warmest room in the house, it's really an efficiency disaster, but we can work through the options on what makes sense once you have it all up and running, including the apparently-plugged zone.

Some boilers simply refuse to die despite suffering morbidity in the form of ever sinking efficiency, but are so grossly oversized for their loads that despite extremely low efficiency they are still able to heat the place. A guy in my office bought a rental 2-family house that was built in 1920, and still has the original boiler, which is probably delivering on the order of ~50% AFUE due to oversizing and age. The sheet metal still looks good- it's practically a museum piece!