put new thermisters on hw/ ch.
still on / off when reaches low temperature, water only warm.
removed inner cover to view other therms at top and run hot water etc.
boiler starts and runs ok then with no cover on.
put inner cover back on and boiler returnes on / off as before
sounds like possibly venturi partially blocked on fan. have been known on other boilers to energise the a.p.s then drop out and removing the cover will maybe be enough to allow the aps to work.
possibility and zero cost.????
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