Vaillant ecomax 824 mystery

[darkhorse0]

Any ideas?

I've got a Vaillant Ecomax 824, approx 8 years old, which was in the house when we moved in.
The hot water temp started fluctuating hot/cold every 30 seconds or so. Online forums pointed towards the secondary heat exchanger being blocked- so I ordered a new one and in the meantime took the old one off and tried flushing it, with no success. Next day one of the connections blew off the SHE and soaked everything in the boiler-that'll teach me to DIY it.
I called in a plumbing company to sort out the mess. They replaced the SHE with the one I'd ordered and also replaced the fan which had been destroyed by being soaked. Everything was fine for a couple of days- hot water working, all good. Then....the same fitting which blew off when I refitted the SHE blew off again, once again soaking the boiler and destroying the fan, cue apologies from the plumbers and a new fan and a refitted SHE courtesy of them.
Then.....that night one of the other fittings on the SHE blew off. This time it was a lower one which didn't destroy the fan, once again, profuse apologies from the plumbers and a refitted SHE, BUT water back to fluctuating hot/cold.
To cut a long story short, they've been back seven or eight times since then, 5 different engineers. They've replaced the pump , flushed the system and replaced a short length of rubber hose in the boiler. They've spoken to Vaillant on the phone and apparently tested all of the sensors. Before todays visit, we had water that cycled scalding hot to lukewarm. After todays visit, which was to replace the short length of rubber hose, we have water that goes from room temp to freezing cold. The hot water temp on the front of the boiler is now rocketing to 90 degrees plus and sticking there for a couple of minutes before dropping- despite the water from the tap being tepid at most.
Before power flushing, it had started making some horrible noises when using the hot water, which I assumed was the water in the primary heat exchanger boiling before the overheat cut out switch activated. Since flushing it sounds perfect, no knocks bangs or rumblings.

Anyone got a clue?

 

[Beerlover]

When they replaced the rubber hose, did they remove the copper tubes and clear them also. There is also a filter on some models, it is in the brass tee below the rubber hose. If this is blocked it will give you the same problems. If you have the model without this tee, they will need to remove thwe service valve to clean this pipe properly.

I'm not berating them, as if they haven't experienced this problem before, they would not know.

So please show them this, and I hope it helps both of you.

BUT if the pipes are clear, you may have a blocked main heat exchanger. Get the manu if this is the case as the part is more expensive than their 'instant cover'.

 

[darkhorse0]

Thanks Beerlover, I'll check for the filter later. Other than just replacing the part, is there any way of checking the flow rate through the heat exchanger to prove it's blocked?

 

[Beerlover]

Yes, use the D codes; press i & + together then go to D40 press i, press i again and gp to D41 press i. This will give you the flow and return temperatures. they should be no more than 24 ° difference, ideally around 15 ° . Check on both CH and DHW operation. If they are both high it is likely the tubes or the main heat exchanger are blocked. If it is only high on DHW it is more thean likely the filter or pipe to the plate heat exchanger.

 

[darkhorse0]

Thanks very much, that's very useful. I'll be checking the codes first thing tomorrow......

 

[Agile]

I think that your connection to the plate HE is an O ring seal and a clip to lock it in place.

If the connection is not fully pushed in then the clip does not properly engage with the slot an lock the connection.

If you are luckly enough to have a high mains pressure that can push the connection off spraying everything with mains water until somebody turned it off.

Sometimes it helps to close the spring clips a little.

You are lucky enough to have had a good firm who took responsibility for the damage when the joint came apart.

Tony

 

[darkhorse0]

Beerlover, you were spot on! I took the pipe off below the rubber section and lo and behold the brass T union was fully blocked with metal flakes- no filter as such, but the bore reduces dramatically inside the T which was where everything was getting trapped. Cleaned out and hey presto, working hot water! It's running hot compared to the setting on the front (ie. if I set hot water to 60 degrees, it runs at a constant 72 according to the readout on the front) but at least it's constantly working!

Can't thank you enough.

Agile, yep that's the connection. Our water pressure is not that high, I suspect the blockage was causing a pressure build up......The company has been really good throughout, (apart from actually getting things working....) It must have cost them a fortune in free callouts to try and sort this. I think they'll be as pleased as me

 

[Agile]

At the cost of supplying you with a free fan I doubt they will be happy apart from ending a disaster job!

Tony

 

[darkhorse0]

At the cost of supplying you with a free fan I doubt they will be happy apart from ending a disaster job!

Tony

That's exactly what I meant, Tony.

 

[Boilerman2]

Darkhorse, it is normal for the Temperature display to read a higher temperature than the Hotwater temp this is because the display is reading Primary water temperature (the water in the boiler) not the water flowing to the tap which will always be a few degrees lower

 

[darkhorse0]

Ah, that makes sense Boilerman2.Thanks for letting me know.....

 

[The831Bunny]

Use D.3 to check the DHW temperature. It reads from the NTC on the DHW outlet pipe at the plate ex.

Press the i button and the + button together. Display will read D.0. Press the + button to advance to D.3. Press the i button to read off the temperature. Press i and + together again to return to normal boiler temperature display.

 

[Agile]

While you are looking at they you can also see the flow and return temperatures to the plate HE at d40 and d41.

That would usually be between about 15-20 C. If it goes a lot higher then its an indication that the plate HE is getting blocked.

Tony