Dave Baker wrote:
The overflow should vent outside and there should be enough downslope on it so
that water can't run back down the pipe. As to why the level rises there are a
couple of possibilities.

Sorry, I probably wasn't clear on that point. The water leaves the
feeder tank via the overflow. The volume of water is so small that when
it gets to the end of the overflow pipe outside the house it goes down
the cross section of the pipe, back along the underside of the outside
of the pipe until it gets absorbed into the wall. I guess any physicists
here will be able to explain it in terms of surface tension?


1) Hot water expands so you tend to find the level in the header tank rises a
bit anyway as the cylinder heats up. Set the float position lower. 3 or 4
inches below the overflow is about right. 1.5 is too close. If the float arm is
plastic there should be an adjusting screw on it and you just bend the brass
ones by hand.

I'll set it to around 3/4 inches below the overflow.

2) If there is a steam vent pipe from the cylinder to the header tank does any
water trickle from that? A pump on too high a setting or a badly installed
system can lead to this.

I haven't seen any water coming from the vent pipe, but I will keep an
eye on it just in case. I'll let you know what I find out.

Thanks for your help,

Andrew