Reverse Circulation

[spacethegas]

is it me, i just posted & then found 7 or 8 more replies.

 

[arildthegreat]

OK. dhw stat turned up. Bypass shut off. All TRVs fully open. radiators do not heat up.

 

[spacethegas]

replace the gate valve with a bypass valve.
it may be necessary to fit a fit an nrv valve as said before.
in the mean time turn down the gate valve all the way & open it 1/2 turn.

 

[arildthegreat]

Apollo Fanfare! Got one myself. They are fairly fussy on the setting of the bypass valve. It should be adjusted so the flow/return temperature difference at the boiler is 9°C. The drop across each radiator should still be 11°C.

Would a bypass valve as you suggest satisfy the "fussy" boiler?

 

[spacethegas]

it is adjustable.

 

[arildthegreat]

Is there a problem having some radiator returns (see first post diagram) between the bypass and the boiler on the main return?

 

[namsag]

Yes as the water then back can feed up them.
The bypass should be the first connection after the pump on the flow and the last connection on the return pipe.
After ALL HEATING connections come into one pipe .
Then this one pipe connects into a tee with the hot HOT WATER return which should not have any tees in it
With the remaining connection on tee running back to the boiler with the other side off bypass teeing into it between the boiler connection and where you joined the HW AND CH returns.

Have a look at the myson appolo 30/50s drawings on www.partsarena.com/baxi very self explanatory just ignore the line for draincocks

 

[arildthegreat]

Thanks for that. Thing is, it is not those radiators that heat up with only the HW on!

 

[namsag]

Are you sure that that is the return for those rads very easy to miss a pipe crossing under floors or even another tee into this pipe underfloor .
But your problem is definetley a return in the wrong place.
I would not fek about with non return valves etc repipe it proper

 

[arildthegreat]

I am pretty sure. The pipes are above my head in a cellar. Four small bore returns from 4 radiators (at the point marked on the diagram). The 4 flows are just past the heating 2-port valve (again as marked). I can trace the ground floor ones (flow and return) to the radiators themselves and the upstairs two go to the first floor, to the 2 radiators up there. These are all at the rear of the house, where the bolier, cylinder are. It is those at the front that heat up with the HW.

 

[D_Hailsham]

The bypass should be the first connection after the pump on the flow and the last connection on the return pipe.

Here is a modified version of your diagram showing where the Bypass should be connected to the return pipe

Untitled

• D_Hailsham
• 29 Jul 2008
• 1

 

[heatingman]

As Namsag pointed out there is only one thing that can cause reverse circulation, bad installation with commons not correctly connected. If you cant easily indentify the heating returns the easiest and only answer is to re-run the cylinder return and by-pass return connection, what ever way you attempt to resolve the problem it will involve quite a bit of work.

John