C.H. return pipe connections

[czb]

In an attempt to improve system circulation, I have been experimenting with pump positions in my conventional open vent 'S' plan system.

In order to simplify the piping, the main CH return, HW return and by-pass return are currently connected very close to each other. This seems to have resulted in reverse circulation. When the CH is off , the HW return is pushing hot water back down the CH return pipe.

I can re-route the HW return nearer the boiler ( these connections are upstairs, the boiler is downstairs) and I could also fit a non return valve in the CH return but I am not sure if this is advisable or should be necessary.

Does the by-pass return have to be the last connection before the boiler?
As I understand it, this valve usually remains closed until both zone valves shut and the pressure of the overunning pump opens this temporary return path to the boiler. Also, can the by-pass be too long? The current one is about 1 metre, but another route I could use would be about 3.5metres.

 

[danielp]

make the cylinder return the last connection , and no bypass cant be to long but can be to short

 

[Bernie2]

The usual way to connect up to a standard open vented boiler is starting at the flow tapping on the boiler.
First tee the open vent, then the pump, second tee the DHW Flow, then on to the rads.

On the Return coming from the boiler, First tee cold feed, second tee DHW return and then rad return.

The by-pass should be fitted after the pump in the flow and then back into the return before the DHW return tee.

Some boiler manufacturers such as Ferroli specify a minim of 3 metres for their by-passes. You would have to check your boiler out.

The by -pass is only really a short circuit to prevent the boiler overheating or the pump burning out if the zone valves shut down or the TRV's all closed. I would advise an auto by-pass.

Hope this helps

 

[czb]

Thanks for the information Bernie2,
My system is much as you describe, however the cold feed is on the flow pipe about 80mm after the vent, before the pump. I understand this is OK for low content , high resistance boilers (Worcester 24Ri).
I'm still unsure on the by-pass return position. Most diagrams show it returning between the boiler and the DHW return. Is that what you are suggesting? Or should the DHW always be the last connection?
I cannot find any info on by-passes except for the simple schematics. Currently the by-pass connects to the return immediatly after the rad. return tee.

 

[Plucky]

I was always told system should go FLOW FROM BOILER > VENT > FEED (WITHIN 150MM FROM VENT) > PUMP CYLINDER RETURN LAST BACK TO BOILER

 

[Bernie2]

Yes!

The vent and feed both together are known as a close coupled for high pressure systems. I have often used it myself, but its not the only way. The way I stated first off is the traditional way.

In the case where a close coupled feed and vent are used on the flow, the by-pass return should be the first tee from the boiler.

Danfoss give some good info as do Honeywell. If you Google them I think the Honeywell is called a DU 144 and the Danfoss ARV 22.

Its best to hear it from the makers of the valves themselves, I agree check it out.