yes thats ok
did it just go from being hot to cold or has it been getting colder over time ?
long shot but i wonder if the heat exchanger is blocked.
thats what don't sound right. can't see why the top pipe is only warm.
the only other thing i can think of is the sensors (thermistors)
one on the pump and one on the heat exchanger one is faulty.
does seem like a block in pump or exchanger.
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