Worcester Greenstar 28i Junior

11 May 2011
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United Kingdom
Hello all.

My 28i junior has scale in the heat excahnger due to the hard water here in berkshire, hot water pressure is now at a dribble. A couple of weeks ago I fitted an electronic descaler and this appears to have made things worse - is it scale comin goff inside teh system and getting clogged in the heat exchanger? The kettle now gets a lot less scale, barely any.

I have been advised to change teh heat excahnegr outright, but am contemplating either paying to flush teh system, or take out the heat excahnger and get it cleaned out.

The boiler has two heat exchangers, primary and secondary, whcih one needs cleaning?

I would be grateful for any advice.
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In your case the secondary heat exchanger domestic water side which needs cleaning.

Even in your area its rare for the plate HE to get scaled up if there is no other problem.

Are you sure you have not had some dripping taps or a leaking washing machine valve?

So should i clean it or replace it as advised? How would dripping taps impact on the water pressure, from 10bar to a dribble?

Is it easy enough for a DIYer to take out the secondary HE and clean it with descaler?

Forget the secondary heat exchanger for the moment.

Remove the DHW flow sensor assembly and check the inlet filter and the flow limiter.
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okay, will give it a go. Is the secondary HE for the DHW and the primary the CH?
The secondary heat exchanger exchanges heat energy from primary heat exchanger to the domestic water. The primary water is also used for the radiator circuit.

FORGET the heat exchanger at this stage...check the filter/flow limiter FIRST.

I assume I isolate the stop cock, drain the DHW, isolate the gas (precaution?) then take off the various bits.

Do you recommend new seals/o-rings?
Not managed to take off the flow sensor yet, but have tomorrow set aside to sort out the problem.

The water pressure is still low, although it has now turned cold. As an experiment I put the heating on last night and it worked perfectly fine, the whole system was hot within 10/15 minutes.

Would anyone suggest ordering in a secondary heat exchanger just in case?
Would anyone suggest ordering in a secondary heat exchanger just in case?

No :rolleyes: Sort out the basics first. The flow limter assembly will contain an O ring...chuck it and see if the flowrate improves.
I have taken out the flow sensor and the 'filter dcw', both are completely clear. Not sure what you mean by the 'o-ring' but if you are refering to the 'flow limiter insert 10lt' I didn't take this out.

Do I consider the heat exchanger at this stage?

if you are refering to the 'flow limiter insert 10lt' I didn't take this out

Yes :) this is the flow limiter...they can also block but a common fault is the degradation of the O ring. They can become contaminated and cause a partial blockage. The flow limiters are fitted to stop dumb customers phoning up complaining of poor hot water temperature if there is too much flow.

I suggest you remove the O ring inside the flow limiter to rule this potential problem out.
Think carefully before attemping to remove the plate heat exchanger, its not as easy as you might think,

If you end up removing the hydraulic block buy some new washers for the primary pipe connections with the white twist fasteners, you also might want to change the PRV at the same time.
It was the secondary heat exchanger!

It was difficult to remove (for the plumber) as the original plumber who fitted the boiler 3 years ago left insufficient clearance below the boiler (only 100mm, not 200mm).

Thanks all.

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