Not related to the bus world & coming strictly from the plumbing world, a mechanical swing gate check valve should always be mounted in a horizontal position. If one should happen to be working in a vertical position - consider yourself lucky!
Ball valves or spring loaded check valves can be installed in any position unlike swing gate check valves.
Why do you need check valves in the first place? I have installed two hydronic heating systems in two different houses, and there are no check valves. I suppose AquaHot has a good reason for them...
JC write this filter number Wix 33109 is the filter cross over number for you Aqua Hot lol and carry a spare
Cliff -I believe that WIX number crosses over to NAPA Gold 3109?My AH frustrates me to the point I bought a 120vac 20g electric water heater because I couldn't get enough hot water out of the AH to do dishes, let alone take a shower. Yet the unit will heat the cabin and engine block fine. Go figure.Grrrr. . Ours make plenty of hot water even on electric since it is the XE model,all is good now with the zone that not was working with a new check valve.That number sounds right for NAPA I just can get a bettter deal with O'Rilieys,the techs tell me the later XE models are not prone to as many problems as the older units lol I will wait and see .