Worchester Bosch E9 Error - It's not the boiler !

[MichaelwGroves]

I have been getting an E9 error for a few years. We have replaced a many parts in the system but the fault persists. My engineer has replaced the Thermistors, main PCB and Auto purge Vent in the boiler and Worchester Technical are adamant it is not the boiler and must be a problem with the plumbing. On the heating side it is Y Plan vented system, we have replaced valve, Pump and cylinder thermostat. I also had reverse circulation which I fixed recently thanks to this forum.
The boiler is a Worchestwer Bosch Condensing 40CDi

So, to be sure the E9 error is an over heat. So I need to establish what is wrong with the central heating to make the boiler over heat. I've noticed that on hot water only it is fine. When on heating it errors. When I've watched it from cold, if the boiler get to max temperature within 7 minutes it trips. When it takes 15 minutes to hit max temperature it works fine. It only trips on start up. I've also noticed recently that I can bleed my highest radiator daily, expelling 5 seconds of fast air.
So I'm thinking maybe it's sucking in air and this is what causes boiler to trip, but i don't want to lead you.But if so from where?

The current system is made of two halves, origional 22mm copper to 15mm T to radiators. The new part is 22mm Hep2o Mainfolds to 10mm and 15mm to radiators. The pump is a Grundfos Magna 25. When I put this on auto the house does not get hot enough, but the boiler does not trip. So I have to set pump at constant flow No.7

I attach an image which show the layout almost exactly, including T's etc. If it looks wrong it may well be, or maybe an inaccuracy in the drawing. For instance, yes the cylinder is bottom feed!
Yes there is an unconventional vent just before the pump due to old pump being under powered and air getting trapped before the boiler. If it looks wrong please say.

I am really lost with this, Worchester are adamant it's not the boiler, and we have replaced all the parts they thought it might be, but I just can't see what is wrong with the plumbing. Any help would be much appreciated.



Thanks
Michael

 

[stevetheplumber]

does this sytem need an auto bypass fitting?is the vent before the pum0p an auto one ?

 

[diamondgas]

Initially I'd be thinking circulation flow restricted somehow? A good suggestion by "stevetheplumber" regards an auto bypass... What's a grundfoss Magna 25? I'll have to google that one! If its an 'intelligent' pump then my attention would be drawn to that too...

 

[MichaelwGroves]

Just checked the installation manual, it says "NB Generally a bypass is not necessary on a Y plan system as one of the parts is open to flow"
So not an exact science, why might I need a bypass?

The grundfos Magna is an intelligent pump, but I'm confident it's not this as it was doing it before the pump was replaced, I was hoping the new pump would fix it!

 

[MichaelwGroves]

Flow restriction is worth a thought, but I can't see where?

 

[Roger Welton]

3 port not flowing sufficient, the 28mm honeywells are only rated at 23kW

 

[vern]

The vent behind the pump is wrong, this will draw in air and cause cavitation of the pump

How old is the boiler please cinfirm it is a 40 CDI and NOT HE?

How big is the y plan valve 22mm or 28 mm?

 

[diamondgas]

Flow restriction is worth a thought, but I can't see where?

The intelligent pump is a flow restrictor!! It reduces speed to accommodate what it thinks is right! That may compromise what the manufacturer asks minimum flow through the boiler (guessing)!

TRV's reduce flow hence the recommendation of an automatic bi-pass. It'll only open should the system pressure build to a certain level. It's design should allow the mi's minimum flow through the boiler I'd imagine, and reduce the potential for 'overheat'!

 

[vern]

The intelligent pump is a flow restrictor!! It reduces speed to accommodate what it thinks is right! That may compromise what the manufacturer asks minimum flow through the boiler (guessing)!

TRV's reduce flow hence the recommendation of an automatic bi-pass. It'll only open should the system pressure build to a certain level. It's design should allow the mi's minimum flow through the boiler I'd imagine, and reduce the potential for 'overheat'!

Its on constant 7 so fullbore! drawing in even more air, plastic pipe on open vent = sludge (unless dosed to the gills with inhibtor which i doubt all that fresh oxygen making even more sludge)

 

[MichaelwGroves]

The boiler is 40 CDi
i've checked valve spec, it's only 22mm and yes rated at 26kw.
i can see this could be a problem, but when on hot water only it works?

Could this also be the reason why the pump when on intelligent mode reduces pressure as it thinks a TRV is always half on and backs off?

The vent directly before the pump is a manual vent, so should not be sucking air in, but again I can vent this daily. Could the system be sucking air in from the tank vent pipe?

I have inhibitor in the system.

 

[Roger Welton]

So the primaries are piped in 22mm?

 

[MichaelwGroves]

Yep, 22mm straight from the boiler, nothing bigger.

 

[stevetheplumber]

40 kw should realy have some 28mm pipework up to the threeway at minimum

 

[Roger Welton]

And I'd be looking for s plan rather than y, maybe with heating circuit done part in 28 also.

 

[MichaelwGroves]

But the boiler flow and return are 22mm, so there would still be a restriction at the boiler. Worchester Bosch also advised 22mm pipe is fine.

We know the Valve is rated at 26kW, (this is the Honeywell recommended size, not maximum) but does anyone know the port size, is it less than the internal dimension of a 22mm pipe? If not then we can assume the flow rate is fine through the valve. Also as previously mention, Hot Water only works fine!