After my usual getting rid of cob webs, leaves etc. my 13 year old heater fire right up again this season. It easily ran for 12 hours and the water was warm. But it stopped with the Heat indicator light out and the service light on with the associated clicking noise. I did more cleaning the next day and it worked for a couple of hours and then stopped. A tech at Pentair deduced it was a water flow problem since it works but shuts off after a while (thus not voltage/gas) and suggested I replace the flow valve assembly. I did that and it ran for six hours before stopping again with the same indicator lights. I think it ran longer than the previous try because the water had cooled down over several days. Anyone have anything like this or ideas whatís happening? It seems more heat oriented than flow oriented to me. Although the unit is old, itís still clean and heats well.