Moved cylinder, re-plumbed, now Hot Water in F&E tank??

[Mike2007]

I installed a new cylinder and re-plumber the primaries as cylinder was in new room.
The primaries used to have a 22mm F&E pipework layout but I chose 15mm for expansion and feed pipes (22mm primaries). I now get hot water in the new loft tank, is this simply because there is not enough water volume in the F&E pipework now?
It used to be gravity on the DHW side, pumped on CH. Its now fully pumped (two zone valves, two pumps) because the new coil is a high efficiency coil in cylinder.

Cheers

 

[Armo74]

If i am reading you correctly you say you re-piped the vent pipe in 15mm,Should be 22mm. A picture of what you have done might help.

 

[ChrisR]

15mm for expansion and feed pipes

You have 1) a VENT pipe, and 2) a feed & expansion pipe.
Vent has to be 22mm.
It's also permitted to combine them into one 22mm, unless the boiler mfr says no.

Sketch and upload a pic of where you have them, in relation to the boiler, pump and valves. You may have got it wrong

 

[Mike2007]

15mm for expansion and feed pipes

You have 1) a VENT pipe, and 2) a feed & expansion pipe.
Vent has to be 22mm.
It's also permitted to combine them into one 22mm, unless the boiler mfr says no.

Sketch and upload a pic of where you have them, in relation to the boiler, pump and valves. You may have got it wrong

What stops the heated water migrating up the 22mm pipe into tank if it does on 15mm? Surely its all about % volume of expanded water stored in system?
Could I couple another 15mm pipe with existing to increase flows to tank?

 

[TicklyT]

Which cold tank is getting hot? The cold water storage cistern or the heating feed &expansion tank?

What order have you connected the feed and vent in relation to the boiler and pump?
Gravity circulation systems were usually piped with the feed and vent on opposite sides of the boiler. That layout is not suitable for a fully pumped system, which have a higher pressure differential between those points.

Pumped systems usually have both the feed and vent connections close together between the boiler and pump.

The vent pipe is purely that - just a vent to release trapped air and gases. Expansion is (or should be) accommodated by water flowing back up the cold feed pipe back to the F&E tank.

The vent pipe should rise high enough above the F&E water level to prevent gravity circulation. An undersized vent may actually promote circulation in the manner of an airlift.

 

[ianmcd]

It used to be gravity on the DHW side, pumped on CH. Its now fully pumped (two zone valves, two pumps) because the new coil is a high efficiency coil in cylinder

Do you really have two pumps??

 

[Mike2007]

It used to be gravity on the DHW side, pumped on CH. Its now fully pumped (two zone valves, two pumps) because the new coil is a high efficiency coil in cylinder

Do you really have two pumps??

I was told high efficiency coils are corregated stainless steel and longer, so this needs pumping back to boiler?
Feed/ expansion pipe goes into return and vent pipe joins the flow pipe into cylinder.

 

[Armo74]

They should both be on the flow from the boiler, It should be vent 22mm, cold feed 15mm no more than 150mm apart then pump. unless it is a combined feed and vent. The vent is also there as a safety measure should the boiler stat fail. The cold feed is classed as the neutral point so if the circulator is on the pressure there remains constant.

 

[swbjackson]

It's probably pumping over if the vent is on the flow after the pump. The cold feed and open vent should be between the boiler and the pump and there should be no isolating valves between the boiler and the F&E tank. What you have done will seriously shorten the life of the system and could be downright dangerous.

 

[Armo74]

No mention of any ABV either presuming you have 2 2 port valves

 

[Mike2007]

They should both be on the flow from the boiler, It should be vent 22mm, cold feed 15mm no more than 150mm apart then pump. unless it is a combined feed and vent. The vent is also there as a safety measure should the boiler stat fail. The cold feed is classed as the neutral point so if the circulator is on the pressure there remains constant.

I know the vent must be on the rise to the cylinder, but the f&e pipe can be on the return if the layout is not close coupled.
I have seen many many systems where my pipe design is the same. BUT, like I say its warm in the header tank for CH. Can it be fairly warm whilst in operation or should that header water be COLD??

Armo74. If the f&e pipe was on the rise to cylinder would that make positive pressure into loft tank? I thought there should be no obstruction (valves, pump) between boiler and coil (and rad circuit can breathe)?

 

[Armo74]

Why not post a picture? that will give everyone a better idea of what you have done.