Another Caleffi ThermoMix Question: Reverse Flow From Return to Bypass?

VelvetFoot

Hi. Based on temperatures I am observing, I seem to be getting flow through the return line to the bypass line . This reverse flow happens when the boiler pump is off, the zone circs on, and the zones are being heated from the storage tank. Is this possible? The bypass line is definitely getting hot. I am thinking of adding a check valve, hoping that the flow just doesn't take another route down the return line, through the boilers.

What I am trying to solve is that when both zone circs are running, one's supply is hotter than the other. When only one zone is on, no problem. I am thinking that there is some recirculating going on and it is cooling off the one zone.

Thanks.

4Johnpipe

Can you post any pictures of the piping? I had an issue that was resolved with a crossed supply and return.

cbrass1915

Good afternoon
Can you confirm with a part number or photo to confirm which item you have installed and inform me if new or existing?
I am assuming that this is the Caleffi Auto bypass.
When confirmed I can offer you all the help you need.
Chris - Technical Manager (Altecnic - Caleffi Group)

VelvetFoot

280175A
I think I've figured out that when the flow reverses in the return header because the zones are being heated by the tank (instead of the boiler), if the thermal insert heats up to the region where there is blending, there is indeed a path for water to recirculate back to the zone supply input.

I did notice that the zone supply temperatures equalized after a while, but that was only after the bypass line became about as hot as a zone return.

My concern is that if I put in a check valve in the bypass line, I will force the flow farther down the return line through the boiler. I guess I won't know until I try.

Unwanted flow in weird ways is quite the phenomenon!

VelvetFoot

Believe it or not, I think I fixed up what was happening without cutting a single pipe! (For a change. )

When I installed the pellet boiler I put in another 1/2" boiler makeup line to the other side of the boiler protection valve to make filling the system easier. I had left both valves open after a recent refill. I believe there was unintended flow to the boiler side of the return line, and thence, a clear path back through the bypass line back to supply.

I tried closing/opening/closing etc, the return side makeup valve and it had an immediate effect.

I love it when things don't cost anything to fix!
Of course, I've declared victory before and had to retract. I'll post if my victory is incomplete!