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Question DetailsAsked on 2/15/2016

What could be preventing the heat boiler from circulating water upstairs to the radiator, frozen pipes ?

New home buyer **yaaaay** :/ Its a cape house and it is equipped with a Weil McLain Series 1 Boiler; its up and running fine except it is only heating the first floor; the base board radiators upstairs doesn't get hot, I opened the bleeding valve on each radiator to see if air/water is circulating, and they both bled for awhile with hissing sounds and water gushing out.

The day after I re-opened back the bleeding valves on the radiators upstairs and nothing comes out, as if the boiler isn't pumping water to the radiators upstairs, so thats when I took a pause and decided to get help. Here's a link with my question and pictures of my setup, thanks in advance for the help guys.

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Voted Best Answer

1) frozen pipe - rare in hot water baseboard systems, but can happen - obviously if house generally freezes due to power outage or such and the boiler is then kicked on with the zones frozen, but also sometimes in very cold weather if the lower zone is keeping the house warm and enough warm air is flowing upstairs to keep that thermostat from activating, so the upper loop does not ever turn on. Generally, in my experience, outside temp has to be in the 0-10 degrees range or lower for a lower-level warmed house to freeze an inactive upper level, just from the heat in the house generally - unless of course the upstairs is actually isolated by doors so can get very cold relative to downstairs.

2) failed zone valve - if you disconnect the live (usually red, or black in black and white combo) wire from the zone valve (so you don't fry it) and then manually operate the lever to open the valve. If that causes warming after a few minutes (circulagting pump has to be running) in upstairs loop, then the power head on the zone valve has failed - or the thermostat is not calling for heat because of bad temerature setting or in a low-temp setback selected period in the programming, dead batteries or corroded contacts, set to A/C or OFF, etc. Also check wires at zone valve and thermostat to be sure they have not broken or come loose.

3) rarely but can happen in systems that have set unused for a long time, vapor lock - you have to flush out the system by draining the loop while zone valve and pump are operating, or at high-point vent as you did

4) system is low on water, so only bottom loop is getting all the flow. Generally but not always, boiler will be boiling noisily when firing, or circulating pump will be gurgling - plus if they are working, air vents should be operating to vent the air, assuming incoming cold water is connected.

For the upper loop - make sure the upper zone valve is open (electrically or manually) and then (being careful about hot water burns) open the drain valve (hopefully there is one - photos did not show) on the return side o the upstairs loop to flush the system - water should come out that freely (perhaps preceded by nasty smelling air if vapor locked or loop is only partly full due to air buildup).


The comments in the referenced blog on the gage are right - after draining system and replacing gage (assuming it is wrong or dead), your pressure in the system should be around 20 psi. If actually maxed out like the needle shows, your system is way overpressured.

Sounds like this might be the case, if it is blowing down at you indicate - that indicates overtemp (either bad thermostat or sometimes low on water so water level is below thermostat) - above about 210-220 degrees when it shuts down after firing, or overpressured. If overpressured, if not due to overheating causing boiling, the inlet valve on the pressure control tank may be bad, or the pressure tank bladder may have failed so it is full of water, so not absorbing the heated water expansion properly. Or may be over-pressured because the boiler is overheating, forming steam which is expanding beyond the capacity of the tank to compensate for it.

However - something indicating low pressure - you said the bleed valves bled off pressure and air initially (did pressure needle change ?) but no water next day - that indicates the pressure in the system is too low to push the water to the top story, or your tank is low on water - which would be a bad thing. Or, if your circulating pump is set for intermittent run (so only runs when there is demand) AND your incoming pressure control is set too low, meaning your boiler pressure is actually about 5-7 psi or less, then the pressure without the pump would not be enough to push the water to the second story. If the pressure in the boiler was in the normal range (check your owners manual - probably in the 15-22 psi range) it would push water to the upper level vents so water should come out even if the zone valve was closed, because the water would flow backwards - up the return line. Check that there is not a zone shutoff valve on the upstairs zone loop piping which is closed. Generally, excepting of course drain hose bibs, all valves should be open on your boiler during normal operation. (Note I am talking as if the zone valves are on the "outbound" side of the boiler / pump - some plumbers put them on the return side to somewhat reduce the long-term temperatures they see (return side is cooler than feed side), but makes little difference otherwise which is "feed" and which "return" on a loop, as long as the zone valve are installed with the flow direction correct, per the arrow on the side of the casing, which should show which is "outbound". Of course, should be plumbed per manufacturer instructions, and reverse flow can result in pooer pump peformance and possible cavitation, but in general use does not make much of a functional difference.

If you have a recirculation loop (extremely likely) on the boiler - a line that comes off the top (usually) of the manifold that feeds the zone valves and then returns (sometimes through a fan/radiator unit heater for that immediate room or garage) back to the return lines manifold on the boiler, do NOT ever shut that valve off with the pump running - it can pressure up the system when both zone valves are closed and cause the blowdown valve to operate due to overpressure.

My recommendation - I really hate to quash a DIY'er's and new homeowner's fervor to really take control and ownership of their home, but you might consider having a Heating and A/C contractor (or Plumber if they are the ones who do boiler work in your area - more a western US thing for that) to service your unit, AND to point out and explain its parts and function to you, and you watch the diagnosis and solution and take notes for future reference - because I think you may have a couple of things needing service here.

Other alternative - run through the above and see if you can narrow down cause and effect and where water is and is not flowing - then come back here for a second round of thoughts using the Answer This Question yellow button right below your question. Also, post another picture of the entire boiler showing all the piping around the boiler - zone valve and reutrn manifolds, any return circulation loop, pressure tank, etc all in one photo.

BTW - WARNING - you said something about turning off the cold water feed because the blowdown valve is operating - do NOT operate with cold water off, and if it causes the pressure to go above the roughly 20 psi range then that is overpressuring the boiler, so definitley the inflow control valve (usually on the bottom of the pressure control tank) would be malfunctioning - or the tank is defective or not pre-pressurized to correct pressure, because there is an internal needle valve controlled by it that regulates the cold water inlet - so sometimes one or the other is bad, sometimes both at same time.

Answered 4 years ago by LCD

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