Reverse Circulation

[arildthegreat]

I seem to have the symptoms of reverse circulation as described in these pages i.e. some of the radiators heat up from the return side when only HW is selected. When CH is turned on, they then heat up normally from the TRV side.

Hopefully I have successfully added a diagram of the accessible parts of the system - does this give any clues? This has always been an issue since we moved to this house - no changes have bben made.

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Link edited so we can see it better - Mod 10
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[spacethegas]

try fitting a non return valve on c/h return before the bypass.

 

[D_Hailsham]

If the pipe marked "not sure" is 22mm it is probably a combined feed and vent from the F/E tank.

The important thing is the pipe marked "from cylinder?". If this is the return from the cylinder, it must be connected to the return after all the rad returns. If there is a rad return between the cylinder return and the boiler, you will get reverse flow.

 

[ChrisR]

How it happens; Blue you want, Red you don't:

 

[arildthegreat]

Thanks for replies. I don't think that there can be radiator returns after the cylinder return. My digram is like a plan of the house really. The cylinder is directly above the boiler at the rear of the house and the affected radiators are at the front. I can't think why there would be any more pipework other than to/from radiators at the front.

The "not sure" pipe is indeed, 22mm.

 

[spacethegas]

is there a valve on the bypass. if so what sort?

 

[arildthegreat]

There is a valve on the bypass - which a wheel turn.

 

[ChrisR]

Look it's easy to tell if it's rev circ - feel which end of the rads gets hot first and mark them.
Then put the heating on when they're all cold. If it's the SAME end it's just the motorised valve letting by.
TRVs can be either end.

 

[arildthegreat]

OK, it is the oposite side - should have made that clearer.

 

[steved101]

if it's only 1 or a few rads getting hot (warm) then it probably is the motorised alve is letting some heated water by when it's supposed to be fully shut.

 

[steved101]

Look it's easy to tell if it's rev circ - feel which end of the rads gets hot first and mark them.
Then put the heating on when they're all cold. If it's the SAME end it's just the motorised valve letting by.
TRVs can be either end.

Try this as it is the easiest way to tell and if the opposite ends get hot first when heating IS on, then you know it IS reverse circulation!!

 

[arildthegreat]

It is all the front of house radiators that get more than warm - the furthest away ones less so. The flow pipe is only hot for a about a foot beyond the motorised valve (conduction?), the return pipe is hot hot.
I have a cellar so have easy acces to the valves etc. The heating flow and return dissapear through brick wall towards the front of the house. Can't really see what's going on there without lifting laminate flooring which has the skirting on top!
Individual feeds/returns to the 2 upstairs (front) radiators are visible - small bore pipes - go up through a cupboard at the front door.

Easy access to 4 rear radiator branches - all 4 small bore pipes feed and returns at 2 manifolds at the points marked on the diagram.

 

[D_Hailsham]

Why tell the OP how to check for reverse solution when it is obvious from their first post that they do?

some of the radiators heat up from the return side when only HW is selected. When CH is turned on, they then heat up normally from the TRV side.

And, if you are still confused:

OK, it is the opposite side - should have made that clearer.

OP
So, the return pipe from the HW cylinder is definitely the last connection before the main return pipe enters the boiler. You need to confirm this by visual inspection; saying "I think so" is not sufficient.

 

[steved101]

totally agree with the last post. but this whole post has been confusing!

 

[arildthegreat]

The HW return is the last connection -immediatley (a few inches) before the return pipe enters the boiler. I agree that it all probably sounds confusing - but these are the facts.

Someone asked whether there was a valve on the bypass. Why did you ask? Could this help in the diagnosis e.g. run the hot water with this closed?