I've got an Ariston Microgenus 27 combi boiler. Recently it's developed
the annoying habit of happily producing domestic hot water for a couple
of minutes, but then shutting down for perhaps five seconds before
starting up again. This means that you get periodic slugs of cold
water, which is especially distressing when showering.

The boiler's thermostat for hot water is on max and just by feeling the
temerature of the flow pipe for DHW coming out of the boiler it does
not seem that it's cutting out on the thermostat, so what else could it
be? It's due its service soon, but I'd like to have some clue as to
what could be going wrong before letting the engineer loose on it.

Martin Pentreath wrote:
I've got an Ariston Microgenus 27 combi boiler. Recently it's developed
the annoying habit of happily producing domestic hot water for a couple
of minutes, but then shutting down for perhaps five seconds before
starting up again. This means that you get periodic slugs of cold
water, which is especially distressing when showering.

The boiler's thermostat for hot water is on max and just by feeling the
temerature of the flow pipe for DHW coming out of the boiler it does
not seem that it's cutting out on the thermostat, so what else could it
be? It's due its service soon, but I'd like to have some clue as to
what could be going wrong before letting the engineer loose on it.

what you need to do is see if the boiler flow is turning off the boiler
and what temp it is doing it at.
also is the dhw heat exchanger working ok.... it may be blocked or
scaled up.
check this by running the water and monitor the temp.of the boiler flow
and return at the heat exchanger.
if it is really hot on the inlet and cool on the outlet and the boiler
is tripping out you have a flow problem within the heat exchanger.
try this and let me know
pete