Back circulation??

[jaydebruyne]

Went to a job the other week and it's been bugging me! In the end the boss went to it and diagnosed it as back circulation.

Basically - 3 storey house. Rads on 3rd floor were hot all the time whether heating or dhw was in demand or not. Rads elsewhere were off when not in demand.

I'm assuming the rads on that floor are zoned, they'd have to be, right?

So I start looking for zone valves. Only found one. Only found 1 room stat also. Turned off the programmer and stat and was till getting 240v on the switched live from the zone valve (I replaced the zone valve before I re-tested it).

To me, there is a wiring issue somewhere as shouldn't be getting anything on switched live on the zone valve if the programmer & stat are off. Or the programmer could be faulty (I didn't actually check this at the time for reasons of not knowing how to at the time - I know now).

I am still convinced there has to be another zone valve somewhere.

So, in lamen terms what is back circulation and why would my boss diagnose this as back circulation. It doesn't make sense to me.

Cheers

 

[tolly]

The cylinder return should be the last tee on the primary return before it goes back to the boiler, if it has not been installed this way then you can find rads heat up when hot water is called for.

What floor is HW cylinder on?

Check the microswitch on 2 ports arnt stuck on, if your not sure if theres another 2 port hidden somewhere you can always look at the wiring to see if theres any extra wiring there that looks like it shouldn't be there if it was just a basic S plan, also you could follow the primary flow off boiler and see if it tees off before MV's and then disappears off elsewhere.

 

[doitmyself]

I'm assuming the rads on that floor are zoned, they'd have to be, right?

Depends on when the system was installed and the total floor area.

So I start looking for zone valves. Only found one. Only found 1 room stat also. Turned off the programmer and stat and was till getting 240v on the switched live from the zone valve (I replaced the zone valve before I re-tested it).

That suggest it is not zoned.

Did you test the brown (to make sure no feed from stat) as well as grey and orange wires?