Vailant 824e Kettling on CH

[buckmoy]

Hello all. Got a Vailant Turbomax 824/e which I've been trying to keep alive for a few years.

It had a diverter valve changed recently by a great gas engineer (as HW had stopped working but CH was fine).

HW is now OK, but I am now getting some bad kettling when CH comes on - boiler fires, temp goes up quickly, boiler stops firing. Rads only getting luke warm.

I expect that some sludge or scale has got into the heat exchanger, and before I drop some more £££ on an expert, is there anything I can try first?

The FAQ has a section on additives, I was thinking maybe adding some Fernox DS40 but not sure how to add it to a combi system - or if it will do more harm than good, how much I need to drain etc. Or maybe get someone to flush it?

Any tips gratefully received. Thanks

(FAQ here: http://www.diynot.com/diy/threads/boiler-central-heating-faqs.175736/page-2#ixzz3ocE7TrfG)

 

[cross thread]

check the basics has he opened the flow valves under the boiler

 

[buckmoy]

Thanks Gordongas, I will have a look (on google and the boiler) to see.

I assumed sludge or scale due to the boiler previously making noise like a prop plane going overhead - but that went away after it was drained to have a new rad fitted. So I guessed it had kind of moved on
Anyway will look

Cheers

 

[buckmoy]

Prob shouldn't have needed to google that, but yes - flow valves are open

 

[Agile]

Do the rads start to get hot?

Makes me wonder if the diverter valve is really moving.

Tony

 

[simond]

If the HW is working normally the main heat exchanger is OK, cause it goes through the same one.

Sounds like airlock or blockage in the CH system.

 

[buckmoy]

Thanks Tony - the rads get hot eventually but it takes ages (about 90 minutes (only 3 rads on circuit, one floor of a house)), as the CH circuit is only being heated in short bursts.

Also thanks SimonD - HW works OK...on demand it gets hot, then very hot, then cools a bit, then very hot again so my guess is that the kettling and resultant burner shutoff (before eventual respark) is happening on HW as well. But the kettling noise isn't as loud, the shutoff cycle is slower. (I will check that when I get home)

Maybe I need to try and get the heat exchanger out and clean it (some guides online, soaking in various acids etc (obvs care needed as to which one)) or perhaps just admit defeat and call in an expert.

thanks for your help, appreciated.

 

[simond]

The secondary HW heat exchanger would fill up long before the primary one. So its not the pump then?

 

[Agile]

Have you set d0 to the minimum ( about 8 kW ) and the anticycle delay to minimum?

To try to keep the burner on for longer on CH !