DHW luke warm, CH fine, combi boiler

[abanana]

Hi,

We have a Worcester Bosch 30CDi combi, about 5 years old. The central heating appears to be fine (rads get hot), but the hot water at all taps runs cold initially (cold water in pipes) then quite hot (but not as hot as previously) for about 5 - 10 seconds, and then settles down to about 36 degrees Centigrade. Incoming mains water is around 6 degrees. Manufacturer expects a nominal rise of about 40 degrees, so we're about 10 short.

This has only happened since yesterday -- things have been fine during the very cold weather right up until yesterday. Since then, the symptoms are as stated above.

Worcester Bosch support line are saying it's almost certainly not the diverter valve, but it could be the NTC sensor (not sure what NTC stands for). But, then, we've spoken to two different techs and the first one had no idea what it could be...

There are NO errors on the display and our friendly plumber (fits WB boilers, but doesn't service them) agrees that the condensate pipe isn't frozen (plus, the boiler should give an error for that).

Nothing else appears to have changed: no sudden drop in mains water pressure, no roadworks locally that I'm aware of, etc.

Has anyone got any ideas as to what might be causing the problem? Anyone familiar with this set of symptoms on these boilers?

Thanks in advance!

 

[spraggo]

NTC stands for Negative temperature Coefficient, and could well be your problem, but the very cold inlet temp will have an effect

 

[abanana]

Ok, thanks for your input and explaining what NTC means -- much appreciated!

I accept that the cold inlet will have an effect, but it's been no colder here in the the past couple of days than it has been for the past 3 weeks, and maybe even a little warmer today -- although I appreciate the temperature changes can take a little while to affect large masses of water/ground. This is, however, dramatically and suddenly cooler water coming from the hot taps -- there was no problem yesterday morning, but in the evening it was too cool to take a comfortable shower.

So if we run with the issue being the NTC sensor, anyone know where I can source one? I've searched online and have found NTC sensors for other models, but not the 30CDi Combi. The GC number of the boiler is 4731193. Is it, perhaps, called something else? I see references to "thermistor sensor kits", but nothing that appears to explicitly be an NTC sensor for that model.

Thanks again for any help!

 

[abanana]

Well, seems that Worcester Bosch spares centre don't have an NTC Sensor listed for the 30CDi (natural gas combi), but they "think it's probably the DHW Sensor", part number 87145000810.

So, their downloadable Engineer's Service Booklet specifically refers to changing the NTC sensor for the A5 fault, their support line thinks the NTC sensor is responsible for the symptoms we're experiencing, but the spares centre don't have an NTC sensor listed? I'm losing a lot of confidence in this company, that's for sure!

Any further suggestions would be gratefully appreciated!

Hope you all have a relaxing Christmas/New Year, too.

 

[spraggo]

Any further suggestions would be gratefully appreciated!

It seems that you have got mixed up with the technical jargon boys, the
NTC was originally described to notate the DWS on vaillant boilers.
In other words the NTC on your boiler is in fact a DWS.

But to confuse matters further they should be called HWS (Hot Water Sensors) as they are used to sense the domestic Hot Water and The Central Heating Water. Hence there are two if them on your boiler and they are both identical. Merry Christmas.
Regards
spraggo

 

[abanana]

I agree that there's some confusion, spraggo! Thanks for the clarification, though.

But, err, what does "DWS" mean? Domestic Water System?

And I take it from what you say, the DHW temperature sensor is, indeed, the part that the Worcester Bosch support line is most likely referring to?

Thanks again!

 

[spraggo]

I agree that there's some confusion, spraggo! Thanks for the clarification, though.

But, err, what does "DWS" mean? Domestic Water System?

And I take it from what you say, the DHW temperature sensor is, indeed, the part that the Worcester Bosch support line is most likely referring to?

Thanks again!

Sorry, Should read DHWS, Domestic Hot Water Sensor.

 

[abanana]

Thanks, spraggo. Fortunately, the part is less than a tenner, so I'll get one, get the plumber to fit it and see if it solves the problem.

Cheers!