I hope that title gave the right impression.
Over the past week I have had to replace an old indirect HW cylinder due to a number of leaks.
I have replaced the old (900x450 - 120L) with a larger one (1200x450 - 162L). It was pretty much a straight swap apart from changing the shower pump connection from an essex flange to a surrey flange. Certainly I have not changed the layout of pipes to the coil from the boiler.
The system is a 1992 vintage Johnson Starley warm air unit 'J50' or something like that with a built in Eljan water heater. The water heater is used exclusively for indirect heating of the water cylinder. The system is 'gravity fed' with the cylinder directly above the bolier displaced by about 2m horizontally. unlagged 22mm copper throughout
There were some fun and games along the way, most notably a stubborn airlock in the coil which I cleared using mains pressure via a hose into the vent pipe in the loft. The system is now 'working' in that I have hot water. However I had never really examined the old system prior to the last week but since giving my undivided attention in the evenings I have noticed something, I think, is wrong.
Flow comes from the bolier into the coil/heat exchanger at the bottom of the cylinder and exits at the top before returning to the boiler.
I think this seems wrong (detrimental to gravity feed, heat exchanger ideally should be hottest at top, flow pipework from boiler needs to be very hot), the diagram here suggests it is wrong. http://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm
I have a few questions
Q1 Is there any way the flow in a gravity fed system can get reversed? Sounds stupid I know but how is the flow normally encouraged in one direction - any valves or just position and layout of pipes and heat exchanger
Q2 Bearing in mind the system seems to work now (and I have *not* changed the setup) how bad is it to have it plumbed like this? Inefficient, slower to heat tank, dangerous.
Q3 Is this 'mistake' common, are there any legitimate reasons for doing it this way and should I change it or am I worrying about nothing