Worcester 28CDi Diverter valve problem

[RichardM]

Hi, I have just had someone (Corgi bloke) replace the diverter valve diaphragm in my Worcester 28CDi RSF combi.

The old one was shot.

We get hot water now, but the problem is we need approx 6-7L/min flow before the valve operates. Max flow is only 9 or 10L/min and the spec says min flow should be 2.5-3L/min.

Is there any chance the new diaphragm is the wrong type, i.e. the valve in the centre has the wrong spring or the holes in it are too big?

Or, could there be a air lock inside the diaphragm housing? I noticed a blanking plug on the side of the housing, is this to bleed air out or just for fitting to other boilers?

Any help would be appreciated.

I still have the old valve so I could compare with a new one, if anyone has some photos of one. I don\\\'t fancy taking the valve to bits, just to find out, yet...

 

[COG]

More chance that it was put in wrong than the wrong type fitted, the spring on the diagphram should be inside the larger spring, if fitted the wrong way it would need a greater load to lift it , either way you should have him back to sort it.

 

[RichardM]

If it was in the wrong way round, the valve in the middle of the diaphragm would not open to let the water flow through.

Looking at the web, there doesn't seem to be any different types of diaphragm, so I was wondering if there could be air trapped in the housing stopping the hydraulic effect.

The installation manual doesn't cover replacing the diaphragm, only the whole valve, but it doesn't mention having to bleed air from a new valve.

There are three springs in total. I think the big one resists the water pressure. This was not replaced so it can't be the wrong type. The diaphragm has two more springs on the shaft. I haven't quite worked out what they do. I presume the diaphragm is designed to move the shaft first, starting the heat and shifting the water flow from CH to the WW heat exchanger, then as the diaphragm moves more, the second spring comes into play. The shaft doesn't move any further but the central valve opens against the second spring to allow the water to flow through the heat exchanger after the heating water has circulated. I think the last spring limits how much the central valve can open.

If this is correct, I would suspect that there is too much water going through the diaphragm in the closed position therefore theres not enough hydraulic pressure. This could be because it's split again, it's been fitted wrong and water is leaking around the outer edge, or the slots in the central valve are too big - i.e. it's the wrong diaphragm. Or there could be air in there thats compressing instead of the main spring...

I don't really want to get the guy back because I don't feel confident that he knows what he's doing. He replaced the diaphragm and the expansion tank on his first visit. Bother were shot. That cost £218.00 all in.

I guess I'll just get a whole new valve if no one has any other ideas.

 

[COG]

You only get one part in the diagphram kit and some lubricant. If it does not sit fully then it will leak BADLY if its up side down it may give the fault you have, I don't no because i've never put one in upside down although its very possible.if its in the correct way then your valve mechanism must also be faulty in that case you will need a new valve either way you need your fitter back to establish this unless you are going to do it your self this time.?

 

[djbunny]

was it a complete new valve, as this comes all assembled and the diaphragm should not be the problem. some cheap diaphragms on the market are constucted incorrectly the spindle is fitted the wrong way round so it is slightly shorter in lengh hence why it needs higher flow rate to make micro switch

 

[doozy]

******

 

[ollski]

The cdi is a dreaded job, it involves a complete drain down and loads of component removal to gain access plus they often leak, its one of the few valves where I would recommend complete replacement for the difference in price.

 

[PEDANTICVINDICTIVEMAN]

By the time you have ****tedd around getting the damn thing off and stripped it, you are better off time/money wise fitting a new valve, the brass plug is to fit the optional Worcester DHW expansion vessel, this is required to stop damage to certain shower mixers.

 

[COG]

That mini expanion vess fiyying is so you can comply to a forgotten building reg, basicly in case the mains inlet expands when in ch mode for a period of time,example would be on a boiler with a double matrix heat ex in a caravan, customer leaves heating on low while caravan empty dhw expands as no taps opened very small pipe work to take up expansion and non return valve in stop cock = dhw pipe expands over 10 bar and POP wet caravan

 

[ostridge]

****

 

[davebgas]

There's a flow adjuster on the cdi div valve. Try setting that before anything else, seen plenty that need it. Apologies for jumping in late and probably missing something