I have an H machine that keeps giving a No Water alarm every few minutes. I checked all the pressures, including the Inlet water pressure regulator, which seems ok. Any other ideas??

Try replacing the float.

I replaced the float switch about a month ago when the problem first appeared, and I thought that had fixed it, but now problem came back. I checked the float switch again today and it checks good. I also checked V41 following the troubleshooting guide and it checked ok. Weird thing is that alarm does not come up when i'm troubleshooting, only during patient treatment. any more ideas??

I would be interested to know what the loop pressure is. Also when the last time the inlet filter screens were replaced (if so equipped). If it will not fail while it is in your tech room, I would check your loop pressure at the station the failure is evident. Please let us know what you find out.

I've had this problem before and it turned out to be the inlet pressure regulator, even though the pressure is correct, the flow through the regulator becomes restricted with age, thus filling the hydroblock slowly causing intermittent no water alarm.
Replace the regulator and go get a beer (after you clock out)

I agree with the inlet pressure regulator also. There is a replacable O ring in those. I think it is the same O ring as the small one on the acid and bicarb wands. If you don't replace the pressure regulator, try just replacing that O ring.

Have heard of trash within float switch chamber causing "NO WATER" alarm. Seems that a piece of tape like obstruction was causing intermittent.

A couple of weeks ago was chasing down a flow alarm with a no water alarm, while checking deair pressure, there seemed to be a lot of air on the inlet side of the deair pump. Checked the deareation orifice and found a couple of pieces of chaff, when removed and replaced o-rings-- problem solved. Hope this helps.

When it happens during treatment and you're able to consistently repeat the reported condition, turn the dialysate flow rate down and see if it goes away. Like someone else said, it's probably a flow restriction somewhere in the inlet or low loop pressure. If it's either of these two, the no water alarm should stop when you turn the flow rate down. If it's a problem getting enough flow, you should have noticed this when you checked the inlet pressure regulator pressure.