Air getting into house hot water loop

Hi all,
I have a hydronic wood furnace that was recently installed soley as a forced hot water heat source. The system was suppose to be installed such that in the event of a power failure the heat on the primary loop would be sent to a dump zone. Well we had a power failure and the heat was not dumped anywhere..hence the TP valve blew many times. As it turns out the dump zone was tied in as just another zone valve but activated by a seperate aquastat. On the house loop, the plumber tells me, the circ pump was cooked because air had gotten in somehow. How can this happen?

Desperately needing heat back in NH

Surely you had this installed by a licensed contractor. Call him back to make the installation right.

Guessing, but a possibility is that the air came out of your water. In general water has air disolved in it. When you heat it up, the air comes out, because solubility of air in water is inverse with temperature. In an unpresurized system, the air will go to the topmost available space.

In a closed system you would have to bleed out the air once in a while, until the water is totally degassed.

http://www.engineeringtoolbox.com/air-solubility-water-d_639.html

plumber

If this is the same guy who installed it, I think he since he cannot dazzle you with brilliance, he is trying to baffle you with BS. Air does not "fry" the pump. AIR without any water can damage the seal so that it either leaks water or sucks air depending on the degree of damage but the pump should still work. If the pump is fryed, it may be because of something he did and he is trying to blame it on something else.

It makes sense to me: if the pump runs dry long enough, the pump mechanism'll get hot, seize, the motor keeps trying to push...


Excuse me for asking what may be dumb question, but: if the power goes off, how's the aquastat for the dump zone supposed to work?

pump

The water normally only lubricates the pump seal so if there is no water it is damaged, but the pump does not overheat. The pump will overheat IF there is water but it is stationary and cannot circulate because of closed valves or other reasons. The the water can heat up to steam temperature and cause other problems, but even then the motor would still run.

hj said:

The water normally only lubricates the pump seal so if there is no water it is damaged, but the pump does not overheat. The pump will overheat IF there is water but it is stationary and cannot circulate because of closed valves or other reasons. The the water can heat up to steam temperature and cause other problems, but even then the motor would still run.

Click to expand...

Aren't a lot of pumps bearings water-cooled and/or water-lubricated?