Bad circulation after new WBosch 18Ri fitted to OV system

[grobsy]

I installed a Worcester Bosch 18RI to an existing open vent system but there is really bad circulation. some rads ok to Luke warm and a couple still cold.

I have been back 3x to bleed air out of the system. 2 rads particularly bad. Air still rattling past pump (located in basement) and boiler. The flow is piping hot, but the return only slightly warm.

System: open vented s-plan, all ground floor, f&e tank quite high (approx 3m). The expansion pipe tees off the flow at the boiler. Can't see where feed, cylinder connections are. All rad valves crappy twin ended type. The customers say it worked fine before new boiler. I have also changed the pump. Was reasonably clean water when I drained it.

Old boiler was wall hung Netaheat cast iron. I have put in pump over-run and bypass (yes I have set this so it it not passing when it shouldn't).

I am therefore wondering:
- can there still be air in it after several bleeds.
- could the system be drawing in air? When I haven't changed the pipes.
- what else could it be?

Any advice and wisdom would be gratefully appreciated...thanks G

 

[Gasguru]

Start ripping the place apart...appears to be blocked pipework...probably around the feed connection or between the feed and vent. Why is the feed (expansion) pipe first off the flow...should be the vent. It may have worked better before on the Netaheat but the Ri will have a higher head loss across the heat exchanger so the pump will struggle to circulate with the partial blockage.

 

[bazdaman]

Did you flush the system or just drain it?.

 

[Dan Robinson]

I suspect the OP has confused his expansion and vents .


In any case - the "get yourself out of the shyte" solution might be to combine the feed and vents at the header tank.


Why people fit these ****boxes is beyond me, but hey ho. They're fine when they're working .


OP - register for the combustion chamber section of the forum where you will get more advice on shifting these aliens

 

[D_Hailsham]

The expansion pipe tees off the flow at the boiler. Can't see where feed, cylinder connections are.

Old boiler was wall hung Netaheat cast iron.

What's the betting the feed is on the return?

OK when the hex was low resistance cast iron, but completely unsuitable with a modern high resistance hex.

 

[jeff the gasman]

Experience counts for everything when it comes to system hydraulics.
Jeff

 

[Gasguru]

There's nothing worng with the Ri. A few installers on here come across a couple of cooked boilers and constantly slag off the whole range. I've a couple of rippled Ri's on the books out of loads of Worcester Greenstars I look after...but they still work fine.

 

[grobsy]

thanks for your replies.

Just to clarify. I just did drain down 2x now but no powerflush, but system looked fairly clean.

I might have confused terminology on use of expansion so to recap -

The order on the Boiler Flow is: Vent pipe 22mm teeing off above the boiler (I think I referred to that as expansion), then pump, then zone valves.

There is no sign of the Feed from the header tank but this is a few meters away from other stuff in another part of the house , so maybe on the return?

So I am also thinking it is negative pressure sucking air down the vent.

 

[jeff the gasman]

The expansion should not be there.
Fook me ever likely I've got too much work.
Jeff

 

[bazdaman]

Im sure there is a pretty picture in that book that comes with the boiler on how the system should be, although im sure you have studied it meticulously if you are fitting the boilers.

 

[gigz]

Go up in the loft and cut a tee into the vent pipe below the tank, now cut the fill and connect this to the tee. Cap the other end (preferably where it joins pipework below to avoid dead legs). I always invert the feed tee.

 

[jeff the gasman]

thanks for your replies.

Just to clarify. I just did drain down 2x now but no powerflush, but system looked fairly clean.

I might have confused terminology on use of expansion so to recap -

The order on the Boiler Flow is: Vent pipe 22mm teeing off above the boiler (I think I referred to that as expansion), then pump, then zone valves.

There is no sign of the Feed from the header tank but this is a few meters away from other stuff in another part of the house , so maybe on the return?

So I am also thinking it is negative pressure sucking air down the vent.

It's not so much pulling air down the vent as trying to push the contents of the system into the f and e tank.
The arrangement you have drops the system pressure to less than atmospheric.Air can ingress at valve stems compression fittings Aavs etc.
Jeff