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Discuss Gravity Flow On Fully Pumped System in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Veggie Dave

I'm trying to cure a fully-pumped central heating system where the radiators become warm when only the hot water is turned on. This has always been the case ever since the customer moved in.

The three port has AB on the left, A to the top and B to the bottom. I was wondering if it's possible the port was allowing some water past it into the heating circuit.

Or...

The return to the boiler from the primary and secondary are a T fitting within two inches of the boiler, with the top of the T being the primary return, the bottom of the T the secondary return, with the combined flow exiting on the right. Could it also be possibly that the primary return is taking the path of least resistance into the secondary circuit?

If it's the second case then a check valve on the secondary circuit should cure the problem, yes?
 
as long as the primary return is the last tee before the boiler you shouldn't get back circulation
 
I'm not sure if it is or not...

vd2.jpgvd1.jpg
 
I would have thought that that close to the boiler would not have caised it to back feed though the rads,( can't be sure not on site) is the three port a mid possition ar a diverter valve? it could be stuck in the mid posstion thus allowing flow though both cuircits of the heating. hope this helps! I can't tell from the out side mid poss or diverter! only the numbers on the end!!
 
It's a mid position 3 port. I'm thinking the most probable cause is the valve, but looking for advice as I'm simply not sure.
 
if the valve is passing you would feal the heat in the pipe work from cold switch on hot water and feel if the pipework to the heating circuit gets warm
 
if changing the 3 port doesnt work then the returns are teed in wrong. no rads should be teed in after the cylinder return.
 
I managed to get back today for a proper look. It seems there are two problems - the 3 port appears to be letting a small amount of water through into the heating circuit but it looks like the primary return and secondary flow are too close so that the return is also heating the secondary pipework.

As getting to the pipework would mean major work in the tiny bathroom I'm not sure what to suggest to the customer. Even just removing the 3 port will be a nightmare as the airing cupboard is only six inches bigger than the water cylinder. Access is, to say the least, limited. ;)

And, of course, the three port is halfway into the cupboard...
 
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check valve on the return?

I don't think that's possible without dismantling the entire shower enclosure to get to the upper return, and digging up the concrete floor to get to the lower return.

I'm probably showing my lack of experience here, but I'm not convinced the way the circuit has been designed is particularly efficient. Personally I would tee the upper and lower returns together before then teeing into the primary return. I've done a quick diagram to show how the circuit actually is at the house.

vd3.jpg
 
It is the pipework that is at fault. It should be done like this.
untitled.JPG
Easy to tell.
Turn on hw only and check which leg of the rads heats first. Then turn on heating. If it is back feeding the opposite pipe will heat first.
 
Ah, so it wasn't lack of experience after all - I was right. ;)

Thanks everyone.
 
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