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Posted by HeatPro on November 14, 2008 at 11:19:38:
In Reply to: Re: Sudden Pressure Loss Baxi boiler posted by Mike Conroy on November 14, 2008 at 09:56:54:
As domestic water pressure is ordinarily in the 3 atmospheres range, and boiler pressure is in the 1 atmosphere range, a leak-through from DHW to boiler side would be the other way around, pressurizing the boiler water and dumping the relief valve. It is ordinary for combi boilers to have stuck water direction valves and leak-throughs are possible in some models.
You might have a domestic hot water screen clog, exchanger liming, or something upstream closing the line off a bit. Liming of the exchanger is something tank water heater owners don't become aware of until they've had an instantaneous water
heater a few years. Such type heaters are disassembled, cleaned and refurbished yearly in European countries.