AAAAAAAAAAARRRRRRRRRRRRRRGGGGGGGGGGGGHHHHHHHHHH!!!!!!!!!!!!!

[jelboy]

Hi guys
I am at my wits end so could use some help please!!
I recently installed a WB 24Ri (OV boiler), honeywell 3 port and grundfos 15/50 pump onto an existing system... It was power flushed, naturally, and all seemed fine... filled it with some air issues, but I managed to clear it all and left the job happy.
The customer then called and said he has no heat downstairs (boiler is downstairs, cylinder pump and 3 port are upstairs) - I went back, bled a bit of air from the system, and by shutting down the upstairs rads managed to get it hot ds again... I balanced it up (us & ds), all rads were boiling, left and thought that was it.
He called again. No heat downstairs again. Upstairs well hot, but none down. I changed the pump to a 15/60 and eliminated the by pass as its not needed with a honeywell 3 port. I filled up again, bled air out of all the system, ran it and it took a while to clear the air but when it did the system ran great! Off I went!
Guess what? He ran this morning - no heat downstairs!!!!
I reckon that circulation is just taking the easiest route (upstairs circuit), and ignoring the downstairs... There appear to be no obstructions, cos it runs fine when it is bled and encouraged to go downstairs, pump is awesome and boiler is cool... No point going to a sealed system as the f&e is full of COLD water and its not pumping over....... SO ANY IDEAS, PLEASE???????????????
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Read more: //www.diynot.com/forums/plumbing/poor-heating-circulation.338715/#ixzz27n87xG15

 

[Armo74]

Bit of a long shot but is this happening when just the DHW is being heated? If so is the return from the cylinder the last one before the boiler? maybe reverse circulation. I take it you consulted the boiler manufactures instructions to see if it required a bypass?

 

[MANDATE]

My idea for what it's worth.
A balancing issue between upstairs and downstairs. so close upstairs lockshield valves by half a turn and open downstairs by half a turn.

Could also be a balancing issue between heating and hot water, sometimes a gate valve is used near where the coil leaves the cylinder to act as a lockshield, closing this a touch may make the difference.

 

[Terrywookfit]

Put a balancing valve in primary flow/return.