Worcester 280 - Hot Water problems are back again !

[webrits]

After fixing the problem here http://www.diynot.com/forums/viewtopic.php?t=123110 with my heat exchanger (or so I thought). The issue with intermittent hot water is back, although it's only done it twice in 2 days. Can sometimes take a while to get hot too.
Any ideas?

Suprisingly the old HE didn't have sludgy water in it after removal although the fittings on the back plate were a bit dirty. Should I have flushed the boiler somehow before fitting the new HE?

 

[DP]

Here is simple advise on how to fix your boiler. Get the manual out and run HW tap. Check operate sequence and establish where the sequence has stopped. Now act accordingly.

OR start changing one part after another. You may just be able to fix the boiler by the time last part has been replaced.

 

[webrits]

Thanks for the tip DP. But that is exactly what I've done !!!
Based on the helpful advice from other posts (see link above) as well as following the fault finding guide I changed the DHW HE.
Initially this seems to have fixed it but occasionally they are reoccurring but to a lesser extent, hence the repost.

 

[DP]

Let the boiler cool down. Then run a hot tap.

Are the two pipe (flow and return) to rads heating up? Check the temperature of water on the middle connection of the diverter (if you can access it) or on the pipe where AAV is fitted (CORGI area I am afraid). Check modulation during HW demand, or the HWHE appropriate connection that lets in primary water.