Combi periodically cuts out on DHW

[Martin Pentreath]

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.

[gasman pete]

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