OpenTherm with two boilers & other related questions

[Jabes]

Ah yes. I have a LLH (actually closely-coupled tees) because the boiler's built-in pump didn't have enough head left after the losses in the HEX.

What's an LLH?
Both my current old Valliant's have their own built in pumps and seem to drive the system ok

Best wishes
James

[mtmcgavock]

What's an LLH?
Both my current old Valliant's have their own built in pumps and seem to drive the system ok

Best wishes
James

Low Loss Header. They're used on larger systems and when there's more than one boiler. You'd have a system boilers that pump into the LLH, then depending on which LLH you have you'd pump separate zones out of the LLH with each zone having it's own pump.