Worcester cdi rsf hot water problem

[JamesCollins]

Hi all

Just a quickie as I have a problem with my combi on the hot water

What should roughly the temperature's be on the flow and return a plate heat exchanger?

The hot water runs ok and then runs cold

I'm thinking it is the plate heat exchanger blocked, or possibly a thermistor fault. There are other things but as I am home now I'd like to try and find the fault before getting it sorted

Any help would be much appreciated all

Thanks for helping

James

 

[Dazman13]

hi i've got the same problem, ive just had the expansion tank,the fan and a valve replaced. the hot water worked for 3 days now the boiler fires up and the ignition light is on after running hot water for approx 1 min it goes cold and the ignition light on the boiler goes out. Heating side works fine any ideas anyone?

 

[ratonnastick]

The most likely cause of the fault you describe is the plate to plate heat exchanger being blocked. There are other common faults with the CDI range the hot water diaphram fails about every 5 years.
If you can attach temp probes to the flow and return each side of the plate the flow temp increases very quickly but the return remains only warm. under normal operating condition you would expect about 10 dec difference.

 

[JamesCollins]

thanks, i will do this and let you know

I had the diverter valve diaphragm changed over a year ago as no hot water ignition occured. It was a bugger, very fiddly and had to remove so much to get at it! Wasn't very nice !!

 

[Blooflame]

If you can remove thepull off cover underneath and just check that the spindle on the diverter is staying extended and keeping the microswitch depressed. If not then it's the diaphragm. Failing that, it's the plate to plate

 

[Blooflame]

OOPS! just noticed your post about the diaphragm

 

[MJN]

If it is the diaphragm (it is easy to diagnose as per Blooflame's advice) and you're up for or considering DIY then there's a walkthrough here which might be of interest.

Regards,

Mathew

 

[Maxsys]

I had the same issues, see my original post here //www.diynot.com/forums/plumbing/worcester-28cdi-hot-water-problems.299152/

This is the reply from Agile on another site but relating to the same issues, and my temperatures as shown on the drawing in the post above.

Firstly the 21 C F/R differential indicates its rather blocked, not as bad as some though. Should be about 15 c typically.

Secondly, there is a big difference between the inlet temperatures and the DHW temperatures. Normally about 10-12 C .

I would conclude that the primary is somewhat blocked but also probably coated with deposit causing the poor heat transfer.

The blockage increases the pressure across the HE and that increases leakage in the diverter valve. Cleaning the HE will probably reduce or stop that leakage.

There may also be lime scale on the secondary side. That can particularly arise if you have had dripping taps.

Obviously it needs to be properly cleaned on both sides or replaced.

I replaced my plate exchanger and problem was sorted, i also flushed the system, and replaced the inhibitor.

 

[Agile]

Thank goodness my advice has proved to be correct!

Anyone who wants to thank me can click the thanks button!

There is usually only one place to diagnose boiler faults and thats in front of the boiler. However, temperature measurements with a CONTACT thermometer ( NOT an IR thermometer ! ) will usually give the evidence.

Tony Glazier