On 3 Feb, 20:39, Chade wrote:
On 3 Feb, 20:07, RobertL wrote:


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.

Makes sense. Is there anyway to confirm?

Wait. It does it when the boiler is set to just hot water and the hot
tap is on. If it's just hot water and not heating, would a pump be
involved?