Hydronic System needs purging


Old 01-24-10, 10:11 PM
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Hydronic System needs purging

Durng the last two months, I have had to purge different zones withing my hydronic heating system. It's a closed system, comprised of three baseboard and 2 radiant heat zones. When the problem occurs, a zone, or the whole system, will not get any heat.

The first time this happened none of the zones were getting any heat. The temperature leaving the supply end of the boiler, until, halfway-up the primary loop, was hot. As I moved my hand up the primary loop it got cold. I shut-off all of the flow to the zones and purged the primary loop, and the hot water started flowing again.

I was thinking that the only way I would get air in the system, is if there was a leak. Is this correct, or could there be other ways air can get into the system?

Thank You,
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Old 01-24-10, 11:21 PM
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What do you mean when you say "2 radiant heat zones"?
Do you mean radiant floor heat? If so, what type of tubing
is installed- barrier, or non-barrier?

You are correct in assuming that if you have air in the system,
there must be a leak. What we have to figure out is if water is
leaking out, or is air leaking in.

Most hydronic heating systems have a pressure reducing valve
(PRV) that keeps the system pressure at about 12 psi. Does
your boiler have one?

Can we get pictures?
Old 01-25-10, 06:02 PM
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Also, If you have the system operating at the proper pressure it would be almost impossible to introduce air in a closed loop pressurized system unless it was there to begin with. I would go over the proper air purging technique first, depending on whether you have zone valves or separate circulators, the procedure differs slightly.

Also, if your 'HI' temp is TOOOOOO high it is possible that the water is boiling (percolating)and creating steam pockets (air) in the system. Check the boiler temperature as soon as the boiler kicks off when hi-temp is satisfied on demand. It should NOT be any higher than about 195. (This happens all too often with ambulances and heavy rescue vehicles in their brake fluid systems too where the brake fluid gets so hot that it percolates and the system requires complete bleeding.)
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