The oven knob on mine goes round continuously. Light stays on permanently as I cannot turn oven off - but the oven doesnt heat as I cant turn the knob to a set temperature

Lyn, September 2009

Previous answers say it all, but try the Plumb Center for a replacement plastic coupling - currently (08/07/13) just 61p incl VAT each!
If they haven't got any in stock they're happy to order for in-store collection in a couple of days. Nothing seems to be too much trouble for such a small cheap part - great service.
Stocked as 'Worcester Bosch Coupling 420601', their product code is 858089.

Peter J, July 2013

ITs just a small plastic coupling that has broken,yes its a design fault! as torque turning switch will in time break the little "legs" off the coupling leaving oven control in whatever position it is at the time of breakage. £3 part...£75 labour/callout! Its only because of the push/pull knobs! a linkage to save making two different length shafts( metal) on the control box; why not make linkage metal as well? then no problem.

jeff, March 2012

most probably the coupling. £2.50 on espares. take the back off and you will see . either coupling dislodged or worn or broke , its easy easy fix,as i did myself hope this helps

andyboy, January 2011

The small plastic coupler between the knob and the thermostat has worn/is broken. Do a search for Bosch 420601. Seem to be a couple of quid though it's possible to get them for about 50p.
To fit them you have to slide the oven out to gain access to the top

CF, April 2010

i now have the same problem with my oven. The knob doesnt seem to be the problem. did you get yours fixed? and how?

Sue, April 2010

Lyn
I have exactly the same problem on a bosch oven - HBN13N, I wonder if there is a weakness in the design. I had the control knob out and the shaft is still free to turn without affecting the oven temp, so I think the problem lies further inside the control mechanism. Did you get anywhere fixing yours?

Dave, October 2009

Equipment knobs nearly always "sit" on a shaft that pokes out through a hole. The knob turns the shaft and the shaft operates the control or valve etc. To make this happen the knob must be secured to the shaft in some way to make it turn - sometimes a D shaped shaft with a spring clip to hold the knob in place - sometimes a grub screw.

Your knob is no longer attached to the shaft - you need to find out what's gone wrong - start by trying to pull the knob off - towards you.

Good luck...

Peccavi, September 2009