First, regarding the dual venting of both tanks.

In all fairness I did this system 22 years ago and first time I only
properly vented the one tank. I ASS-U-ME'd that the two connecting/transfer
pipes would allow the air back into the unvented tank... WRONG ! The first
time I drained the system (during the installation) I popped my head into
the loft and 14.7 psi on the outside and 0psi on the inside of the tank had
done its job and crushed the tank. We/I learned from that and put a hole
through 23 inches of Granite to get a vent pipe through and back to the cold
water source tank. Problem solved.

The motorized zone valve, switched with the pump, seems to be the logigal
answer. Beleive it or not I did buy one some seven years ago but.....

If I put the immersion into the upper FIRE tank I would not have any hot
water in the lower IMMERSION tank unless I used the transfer pump. The idea
was to get a second load of hot water into the IMMERSION tank from the FIRE
tank quickly, rather than switch the immersion on again.
The whole problem is caused by this 23 inch Granite wall that virtually
splits the house and the distance between the two tanks. I have to have the
FIRE tank right above the fire so that the pipe run to the indirect heating
loop is fairly short.

Thanks for the "Swing Valve" pointer, never knew they existed. Why only BSP
fitting? Are they more of an industrial device.

Thanks again guys. This is a great board.


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