Worcester Bosch 24 CDi Combined - no hot water

[MrSmile]

Hi all

I have been mulling over a problem while on holiday and hope one of you might be able to help.

Our 24CDi has developed a fault. The central heating works fine but when we turn the hot water on we get warm water at best but within 30secs it is just cold. This is not nice for those early morning showers!

I have done some basic checks such as power and water supply - all fine. i have also turned the central heating side off and turned the hot tap on but it makes no difference. I have followed a description on another website and observed (in the micro switch box) the spindle extending when the hot tap is turned on. It extends every time the hot tap is turned on but the boiler will not fire up to heat the water. The led on the front does not come on and is not flashing. A reset has also failed to solve it.

Any suggestions?

Your help is very much appreciated.

 

[Agile]

Have you measured the resistance of the temperature sensor?

Tony

 

[petertheplumber12]

It would need to be going hot and cold for the cause I have given correction for. If it isn't getting hot and cool repeatedly then the thermistor is the other pos that was mentioned already.
It sounds like classic case of sludge build up in the primary circuit of the secondary heat exchanger. If you put some sentinal X800 in the system, hopefully via the magnaclene, if you have one and if you don't get one. The once added run heating for a few seconds only to get the chemical in the boiler, then run hot water tap for a good while, it should start getting better until its back to normal. Then after a week you can fill and drain at the same time, add inhibitor and it won't happen again.
If i am wrong then I would like to know what the cause was.

 

[moresby40]

more than likely to be the h/w diaphragm,if the hw indicator light has not illuminated it means the micro switch has not made,unfortunately not the easiest of things to change

 

[McCombi]

You say spindle comes out, but does it actually make the switch in the black plastic housing? Does the tap indicator red light on front of boiler come on?

You can remove the black box and manually press the switch with water running to check.

 

[petertheplumber12]

more than likely to be the h/w diaphragm,if the hw indicator light has not illuminated it means the micro switch has not made,unfortunately not the easiest of things to change

That is more likely than mine for sure.and good luck with that one.

 

[MrSmile]

Thank you all for the responses. Very helpful.

Agile - I have not measured the resistance of the temparature sensor. I will do this. I assume I am looking for a consistant resistance or signal to be reaching the sensor?

moresby40 - the h/w indicator light does not illuminate. I will remove the black box and manually press the micro switch and see if the h/w indicator light comes on and if we get h/w. If it comes on then I guess I will be taking on or asking an engineer in to change the h/w diaphragm. I am sure I have read that the cost of this part is £120 or £200. What sort of labour charge would I expect from an engineer to fix this? I have read that this job will take about 2hrs to complete. I am an experienced DIYer with good patients and common sense when it comes to these kinds of tasks but I also recognise the benifits of leaving an experienced engineer to take on certain jobs. I do not want to be ripped off or have an engineer tell me that lots of things need to replacing unless they seriously do. I am moving house soon so this is a fix to get us thorugh the next few months while we finish doing up the house.

Any help on this is very much appreciated

 

[45yearsagasman]

The diaphragm kit can be had for approx £15 or so. This may be of help to you if you go the DIY routehttp://www.newtonnet.co.uk/house/boiler/

 

[CombustionGuy]

or get a RGI to do it

 

[MrSmile]

Thanks for the link it was really helpful and the pictures are a great help. I have read it a few times and I will get the parts priced up before deciding which route to go I.e DIY or Engineer

I will let you know how I get on.

Thanks to all who responded.