Noisy Worcester

[Sid Viscous]

Hi guys, been to look at an old 35CDi II. Works fine on c/h, but open a hot tap.... boiler fires, heats up, starts knocking, pressure gage jumps about a bit, then it goes out. 10 secs later starts all over again. The pin in the diverter moves across ok & stays in dhw position while ever a hot tap is open, moves back fine when closed. It does this whether or not the heating's on. Don't know if this is normal for this model but when c/h is on & you open a hot tap, both c/h and dhw lights are on. Most other boilers I've come across switch between the 2.
Any idea please

 

[albatross]

Sounds like a blockage maybe or a slow pump.

 

[Millsy 82]

I'd be looking at the phex sounds like it's totally clogged up.

 

[GrahamM]

I would be looking at sticky div valve first then looking at plate chocked up. Should have about 10-15 deg difference across the plate.

 

[Sid Viscous]

Hmm, don't like the sound of any of those! I'll check 'em out though. I'm gonna have to get myself on a course soon!

 

[arran197]

You could have an issue with that diverter valve, if the ch is off does it start to pass down the heating when you run the tap? I've had this before on Duo Tecs and it's been the diverter and the plate. All the signs of a dirty system. Basically the boiler tries to heat up the dhw, but cause of the diverter slightly letting water through and the plate being blocked, it can't so starts to kettle.

 

[buckley plumb]

you can pull the diverter actuator motor off and operate the diverter by hand to eliminate that. then check the plate. as above you could check for temp diff across the plate but never had much joy doing that

 

[Sid Viscous]

As I said in OP, you can see the pin on these from underneath & that's moving full back & forth & staying rock steady all the while. So is arran saying look for a bit of heat down the flow pipe with c/h off?

 

[Deleted member 32524]

Put it in hot water only and if the flow/rtn get any heat down them the divertor is passing. Is the dhw thermistor ok? What about flow switch?

 

[buckley plumb]

from what I was told on the course if it is passing due to worn diverter seat the diverter arm can be turned 180 degrees as temp measure

 

[arran197]

That's right, but from experience the diverter valves rarely pass on modern Greenstars so I would be pointing more towards the plate.

 

[buckley plumb]

I would agree plate

 

[village idiot]

strangely enough, I did a service on that same model yesterday. Custard complained that it doesn't heat up as fast as her previous house? She bought the property and moved in on Monday.
I told her it might be due to sludge or a scaled HE. She then wanted to know how old the boiler was? I said about 12-15 years? Really, she says?

So in her presence. I phoned Worcester Bosch. The staff on the line just kept telling me that they have all the parts, so there should be no problem. Custard wasn't interested. She WANTS ME TO BOOK HER IN FOR A NEW BOILER WHENEVER I HAVE SOME SLACK TIME?

Now, we need more proactive customers like this.

 

[GrahamM]

you can pull the diverter actuator motor off and operate the diverter by hand to eliminate that. then check the plate. as above you could check for temp diff across the plate but never had much joy doing that

Is this not the old 35cdi II rsf we are referring to? Not the newer greenstar model!

 

[buckley plumb]

Is this not the old 35cdi II rsf we are referring to? Not the newer greenstar model!

sorry did not read fully yes it is

 

[arran197]

Guilty as charged. Sorry.