Ravenheat RSF100ET

CH operates without problem

The DHW developed the following problem earlier this evening

DHW short cycles on & off in (roughly) 30 second bursts. This can be
'cured'if the DHW control on the front panel is backed off to about 40% of
its full value - which reduces the temp. at the taps to tepid. At first I
thought this was an overheat problem but the overheat stat (which is
resetable) has not tripped. The mains water pressure is unchanged so I have
initially discounted low pressure problems. We live in a soft water area so
no scaling problems.

Could this be a thermistor problem ?

Neil