intermitent hot cold waters

[Dror]

We have Ariston microGenus which was installed in December 04. Recently when we open the hot water the pilot flame switches on but then after a few seconds it switches off for a few seconds and then on again and so on. The result is that the water temp keeps changing from hot to cold to hot and so on. The radiators seems to be working fine.
Any ideas as to what can be the reasons for that and how it can be fixed will be greatly appreciated.
Thanks.

 

[ricarbo]

Has it been serviced? if not atart there.

 

[Dror]

Thanks for your reply. We had a technician that came and said that it is because of a too low water pressure and nothing can be done. You think a general service will do or is there a need for something more specific. It is no longer under guarantee.
Thanks.

 

[ChrisR]

If it were low water pressure your cold would also be very poor. You said "recently" - has the cold changed?
What's the actual hot flow rate from the bath taps, H & C separately, in litres per minute? Use eg a 2 gallon (9 litre) bucket.

Poss reasons for up/down temps:
flow rate is really really low, less that 5 litres per minute, say
fault in the boiler like a temp sensor
sludge/old radiator scale in tap water heat exchanger.
Most common, is the last one.

 

[Dror]

It was a flow problem. There was something wrong with the main supply and when that was fixed the hot water are ok now.
Many thanks for the advice.