Reverse Circulation

[D_Hailsham]

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

Thanks for the support

My impression is that many posters do not bother reading the whole topic but just the last post. A bit like butting in to a conversation.

 

[D_Hailsham]

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

Is there any possibility that one of the radiator returns has been teed into the HW return?

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?

He was probably thinking that, if the valve on the bypass is wide open, it will act as a short cut to the CH return. You need a bypass as you have separate valves for HW and CH. What boiler do you have (make and exact model)?

 

[arildthegreat]

I really can't see any possibilty of radiator returns teeing into HW return. See my diagram - those affected radiators are at the opposite end of the house from any of the HW plumbing.

The boiler is Myson Apollo Fanfare - can check exact model when I get home.

 

[ChrisR]

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

Because the OP is still wringing his hands instead of getting on with what he has to do.

It's piped up wrongly, ok?
So you have to expose and do some repiping, or NRV(s) , which are usually easier but pose a maintenance issue. End of.

There's no point telling us which end of which wall pipes disappear into.

 

[arildthegreat]

Thanks ChrisR. I'm wringing my hands at my day job at the moment!
I know it's not enough information, but from the diagram in the original post. What possible scenarios are there? All of the rear radiators are accounted for (no problems with these). Why on earth would the (affected) front ones (there are 4, 2 upstairs and 2 downstairs) be anywhere near the HW pipework. All have small bore piping (about 8-10mm). The upstairs two are accounted for - 2 feed and 2 return rising from the main flow/return in the cellar via that front door cupboard and heat up as expected from reverse flow!! i.e opposite when HW only on and CH on.
I am not in the trade, I've had someone out - he couldn't help. It has been great to have these replies so that I can be better informed when I (soon) get further help from a pro.

 

[ChrisR]

If the known facts provide no possiblility of the behaviour occurring, but it does, then those facts are NOT known!

Maybe there's something connected to the "don't know" pipe? Bathroom rads are favourite for that.
Can you disconnect the return pipe from the cylinder at the cylinder, and take it straight back to the boiler?
I assume you can't see all the present one?

 

[arildthegreat]

Thanks, I'm really grateful for your time.

No its not visible and probably beyond my competence. However, the bathroom radiator is one of the 4 where connections to the feed and return are identifiable in my cellar at the points marked in the diagram. These 4 have never been affected by my "problem"

 

[D_Hailsham]

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.

I take it the boiler is on one floor and the cylinder is on the floor above. So the radiator return pipe(s) will Tee into the return from the HW cylinder. Like this:

View media item 3240
If the wrong type of Tee was used, could there be back flow from the cylinder to the radiators, even though the cylinder is the last connection?

If the known facts provide no possiblility of the behaviour occurring, but it does, then those facts are NOT known!

Ah! The known unknowns and the unknown unknowns.


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.

 

[ChrisR]

Could be gravity circulation OR a side effect of pumping the HW. Maybe?

 

[namsag]

First question should be has it always done it or is it a recent issue .
If it has always done it or has done it since additional rads added and there is no heat getting past the motorised valve then it is a tee in the wrong place .
Especially as you say the circulation reverses when heating selected.
Dont know what d hailsham means by a wrong tee being used a tee is a tee.
Some systems can be a pain to trace back even for a pro but if motorised valve is not passing then you must have a tee in wrong place.
The single pipe from boiler is more than likely combined cold feed open vent that was recommended on appollo installs but you need to find where this goes to take it out of the equation

 

[D_Hailsham]

Dont know what d hailsham means by a wrong tee being used a tee is a tee.

I was thinking of a swept T installed the wrong way round, so it sweeps from cylinder to rad return instead of from rad return to boiler.

The single pipe from boiler is more than likely combined cold feed open vent that was recommended on appollo installs but you need to find where this goes to take it out of the equation[/quote]
That's what I said earlier. The Apollo instructions give the combined feed/vent as the first option but also allowed a close coupled feed and vent, provided they are no more that 150mm apart.

 

[namsag]

Swept tee would not make any difference (power of pump would overide effect) even if they ever made them in 22mm copper.
The comment about combined feed was for the OP to check.
And yes i do know there is two ways to install it ,that is basic . Combined cold feed was recommended on most low water content boilers.
If his drawing is right it is simply a return tee in the wrong place

 

[arildthegreat]

Thanks all. The single pipe from boiler IS the combined cold feed open vent. I have "drawn" a diagram of the returns at the boiler. The HW return is right at the boiler. View media item 3252
Closed bypass solved the problem with the front radiators. Return pipe hot between bolier and bypass.

I'm almost 100% sure that all radiator returns join main return before the HW return.

Is the positoning of the bypass vital? The digram in the boiler manual has it between the HW return and the bolier.[/img]

 

[namsag]

Closing bypass should not affect the rad circuit in anyway if it is it means something is piped in wrong. Turning it off should not stop any rads from heating up
The bypass is there to take excess heat away from the boiler on pump over run or if sytem has trvs closing down to keep a minimum flow.

A properly piped up boiler needs the bypass open otherwise it can cause pilot to trip out or boiler overheat to trip

 

[spacethegas]

turn the dhw stat up. shut the bypass off.
do the rads still heat up ?