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Supply and Return Water Temperature off DHW
Dual temperature guage (generic image attached below) placed on boiler's supply/return pipes shows, during DHW cycle (always on priority), the temperature difference between supply and return water does not exist at all lately. Zone heating, however, seems fine and shows usual temperature differential in supply/return water.
We have a zone valve system for the zones and DHW with one system pump on the boiler
Operationally, while everything seems ok, this's not our usual reading that we can recall. Typically, the difference is around 15F to 20F specially during the 1st minute or two after DHW first calls for heat and gradually narrowing towards end of cycle.
Right now, differential temperature is fairly equal or close within 5F for the most part as if there is no heat transfer/pickup by the HW tank. But yet we get hot water supply as normal with no delay or anything. Are we worried for nothing or something has gone wrong?
Any tip or advice we need to look would be greatly appreciated. Just wanted to educate myself before calling in a pro.
Thank you very much in advance.