In article ,
Sam writes:
Hello,

I would like to upgrade my gravity hot water system to a fully pumped
one. I have been reading the faq and honeywell diagrams.

Should I use two 2-port valves (1 CH; 1 HW) or should I use one 3-port
valve? Using a 3-port valve halves the cost but the faq said 3-ports
were more unreliable. How unreliable are they?

Also, with a 3-port valve you always have an open path for
anything like pump run-on timers. With 2-port valves, you
may need to make special provision for this.

Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs? It might be useful to
run CH upstairs only overnight on a low thermostat setting, just to
keep off the chill; it would be a waste to heat downstairs when
everyone's in bed. Are there any other times it would be useful and
worth the expense?

It can be. Depends on size of house and usage patterns,
and how long it takes to heat up and retain that heat.

I am unsure how to wire a 3-port valve. The 2-port seems
straightforward and has a built in switch. I am not clear that the
3-port valve has a switch to signal it is open; does it?

A 3-port is always open somewhere. It has a built-in switch
to signal the normall closed side being open. I believe there
are standard wiring diagrams for the different Plans on the
web.

The pages I read suggested connecting the orange wire (only B port
open) to the pump. I'm sure I have misunderstood because if that's the
case what switches the pump on when you use port A only or A and B?

There seems to be some controversy: should CH be port A or port B, and
why should it make any difference? Is it that the valves fight against
a spring and that as long as the B port is open the mechanics are
fighting against the spring?

Is the idea that CH is on port A which is unenergised and the HW is on
port B, the theory being that the HW will warm up quickly so that the
valve is not energised for long? If so, does this mean that using
2-port valves is more energy inefficient?

I think it's usually H/W on A and C/H on B. This is to fit in
with the standard wiring diagrams. Turning it round the other
way might require addition of non-standard parts such as relays,
and confuse the hell out of anyone coming to repair it.

I use a 3-port valve to switch separate upstairs and downstairs
heating zones. I put downstairs on A and upstairs on B, on the
basis that if it broke I can still heat downstairs, and that
indirectly heats upstairs to some extent. Also, downstairs is
heated more than upstairs, so the valve spends more time powered
off than powered up with the synchronous motor stalled.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]