On Feb 3, 8:02*pm, Chade wrote:
On 3 Feb, 19:09, "John" wrote:

"Chade" wrote in message

What might it be?

Where is the needle when the boiler is cold?

Just over 1 Bar, which is in the normal range.

Is it possible that the circulation pump has failed? The water is not
circulating through the heat exchanger. the water then boils making
the bumps and leaps in pressure that you see. the flow thermostat
takes a while to register because there is no flow. When it does it
turns off the heat.

Robert