Moved to a new house that has a hydronic heating system for the garage and attached greenhouse. The system consists of a 30 gal. Water heater filled with RV antifreeze running to black rubber tubing inside the concrete floor of the garage and greenhouse. There are 2 zones, 2 thermostats, and 2 Grundfos 1/25 pumps. There is a fill tube and small expansion tank attached to the water heater, and spigot in the greenhouse to purge air from the system.
Local contractors refuse to work on it, but have said it is a decent system.
I’ve tried to purge the air out, by adding fluid at the water heater and opening the spigot with the pumps off. Quite a bit of air has come out, but the system still has problems. The pipes to and from the pumps are warm, but the supply line is cold. The fill valve is closed but air hisses out when I open it.
The pumps are humming but I can’t tell if they are actually working.
I’m not sure whether to order new pumps. Continue to try purging or what to try next.

Purge until ALL the air is out.

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

you really need pressure to purge the air out.
there is a way to do this using a pump to pull the antifreeze out of a 5 gallon bucket and inject it into the system.
you then have a hose on the purge valve to recover the antifreeze back into the bucket.
yeah at first there will be bubbles and air to deal with but eventually you will get all the air out.
i can't get into more detail without seeing what you have there.
but, it can be done.
basically, you pressurize, purge the air, pressurize, purge the air until you get to a point where you can run the pump constantly while letting antifreeze out the purge back into the bucket

I’ve been pouring antifreeze into the fill tube on the water heater, then refilling the gallon jugs at the purge sill cock. About 15 gallons worth so far. The water coming out of the purge eventually starts to feel warm. The water heater is 30 feet from the purge valve.



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it is really hard to see EXACTLY how the circuits are set up.
it appears that you have one zone, 2 circuits and 2 circulators. one circulator is pushing and one is pulling.
as i said...
you need to close the opening in the pipe you are filling from.
you need to hook a washing machine hose to the drain on the water heater so you can attach a small pump that will suck the antifreeze out of a 5 gallon bucket and pressurize the system. a gauge will be needed so you don't over pressurize. then open the purge valve to release some pressure. this will blow out the contents of the piping. this liquid will have air mixed in it.
take that liquid and pour it back into the bucket and repeat.
ideally you would have a hose running from the purge back to the bucket so you could turn on the pump, push some antifreeze into he system (thru the bottom of the water heater), this will build pressure in the system. then you carefully monitor the gauge while opening the purge valve just enough to keep antifreeze flowing but not letting the pressure get over 30 PSI but not letting it get to zero.
alot of bubbles will come out at first but by keeping the return hose aimed high in the bucket so you don't suck too many bubbles back and the hose from the pump at the bottom of the bucket, you will eventually get a nice clear flow.
sound complicated but it really is pretty simple.
lastly, change the water heater relief valve to a 30 PSI boiler relief. the one that is on there now will allow way too much pressure to build and you will blow a seal on the circulators as they are not rated for more than 30 PSI.

I have managed to purge all the air from the pipes, but found that as the system cycles it is losing anti-freeze. I’ve had to add a half gallon each day.
I am thinking of converting the system to baseboard hydronic heat, using the same water heater, and one of the two pumps. The copper supply and return pipes are in good shape, thermostats and electric to the pumps also already there.
I saw a 10 foot baseboard unit for around $500 that I think will do the job.

Make sure the water heater can run at a temperature that allows decent output from the emitter. You also have to know that the output of the emitter is enough to heat the space. The only way to know that, is to do a heat loss calculation for the space. If your space needs 10000 btus/hr and that baseboard you're looking at can only produce 4000 btus/hr at 140 degree average water temperature, you'd be wasting your money.



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