loss of pressure

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    Vaillant 837 - Pressure drop once DHW is turned on, heating also working but have to manually be turned on whilst connected with thermostat.

    Hi, some desperate assistance required please. So, recently come to address an issue where the Vaillant Boiler 837 has had isolating valves fitted, since then, when DHW is used, the boiler pressure drops, as if the water that holds the pressure is released in hot water. also, when I turn the...
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