I have been going at this problem for weeks now.. I reworked my boiler piping to add 2 more zone pumps for the 3 zones in our house. I removed zone valves/motors and now use an ARCO contoller for the thermostats/pump operation which works fine and an L8124 aquastat that runs the burner only.

But!! 2 problems..

1. The aquastat (tried a few of them with the same results) won't allow temps. at the gauge to rise above 150 deg. Pressure is fine. I did static tests in hot water and the (several) L8124 seems to be working fine.

2. Especially on recent warm days, I can't control convection/flow from the boiler to the zones even when I turn the high/low down on the aquastat. Oddly, the 2nd floor zone with the highest baseboards being the worst. In other words, with the pump motors off, I am still getting a large amount of heat in the pipes (especially the 2nd floor) such that I can't control zone temps on warmer days and it is 75 with nothing on with the thermostat at 65.

I added flow valves in proper direct on the outward pipes to no change. I suppose I can add the zone valve motors back again to stop unwanted flow (where is it coming from??) but that is a last resort. My father has the same set-up with 2 zones in a ranch (my little tudor is 3 floors up) and he doesn't have this issue.

Please help!!!

TIA,

Chris