pressure dropping on openning the hot water in my ravenheat csi 85 aboiler?

my ravenheat csi 85t aaa working fine on heating but when hot water tap is opened the water pressure starts dropping and when below 1, it switches off.
A. Q. AWAN, April 2018


done
My guess is your external filling loop valve is in the open position

Continuously pressurizing the system

Do you have a leak somewhere?

When you run the DHW the pressure drops off

?, May 2018
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