Vaillant Turbomax 282E hot water cycling

[aris]

Hello.

I have a Vailliant Turbomax 282E which is exhibiting some strange behaviour with regard to Hot Water supply. Central heating appears to be fine, but when DHW comes on, it comes on for about 20 seconds - then slowly the burner starts getting lower and lower until it is switched off. About 10 seconds later it fires back up.

It is as if a thermostat is switching the DHW off when it gets too hot, then regulates the burner until it is switched off - then as the cool water passes through the boiler, it is re-ignited to come back up to temperature.

Sometimes, the boiler doesn't come on at all - this seems to happen more often when the CH is switched off.

Looking at the installation and servicing guide, I see two thermostats - an NTC sensor and an overheat themostat. The NTC sensor is in the combustion chamber, and since CH seems to work fine with no cycling - i'm assuming this is ok (and also the manual says this is a highly reliable component).

So my other option is the Overheat thermostat.

Any comments on the above symptoms?

Thanks,

 

[bengasman]

forget the stats, your system is full of shyte; needs cleaning.
See faq

 

[aris]

Forgive my ignorance, but I checked all the faq's in this sub-section and did not see anything that might be relevant. Perhaps i'm looking for the wrong thing? Could you point me in the right direction?

Many thanks,

 

[kevplumb]

the domestic hot water heat exchanger is full of shyte

was what he meant

 

[bengasman]

forget the stats, your system is full of shyte;

Sorry, that is a technical expression
In layman's terms:

Your (heating)system seems to be suffering from corrosion, and the debris it has produced is clogging up your plate heatexchanger, aka secondary hex.
There are several ways to counteract the problem and details can be found in faq.
Have a look in both plumbing faq and heating/boiler faq; it is being reorganised at the moment and I don't know by heart which bits are where.

 

[aris]

Ok, I must be daft. I could not find anything about secondary heat exchangers in the FAQs.

I do see a DHW heat exchanger in the installation guide - Vaillant part no 06 4950

I suppose I could replace this - but i'm assuming there is a way to flush it? Can it be done without removing it from the boiler?

Thanks,

 

[bengasman]

Seems that I am the one hallucinating, or admin removed it from faq, and have not added it to heating faq yet.

Will describe process needed later, but must first attend urgent heating issue; my beer is getting warm.

 

[aris]

Haha - no worries.

I did some googling and found some info on another site. Looking at the DHW heat exchanger, it is pretty simple to get to (probably the simplest thing in the boiler) and not so bad to replace - but I do need to drain the system down which is a bit of a bother.

Is there any chance one of the Fernox or similar central heating cleaners may resolve this, or would that just be a waste of time?

 

[mickyg]

If you are gonna change it yourself make sure you get the right one. There's 2 types for that boiler, they are easy to tell apart if you know what your looking for. You can try putting some chemical into the system, It might work it might not! Something like X800 would be your best bet, but you'd have to make sure it got a couple of hours circulating through the plate he. Might aswell flush the rads while your at it, seeing as thats where the problem started.

 

[aris]

Thanks for the feedback Mickyg.

You say there are two for that boiler - do they both have the same part number? The 282/1E installation guide gives it as part number 06-4950 - and I have found this on various online parts retailers - it costs about 90 quid with shipping. Can anyone recommend a good place to buy it?

I suppose I could use the heavy duty stuff - but what about the regular cleaner like X400 - could I put that in and just leave it for a couple of weeks and see? The X800 does not appear to be available in a concentrate which is easier for me to add via radiator.

 

[mickyg]

you can try X400, personally I don't find it that great. X800 is much more effective. You could always drain a radiator,remove the vent plug and funnel it into the rad. The part number you qouted is by far the most common one and likely the one you need, but I know people who have been caught out...
where abouts are you btw?
here I've done you a nice picture

Untitled

• mickyg
• 30 Apr 2009
• 1

 

[aris]

Hi,

I am in Hertfordshire. I'll take a look at it and make sure I get the right one, though i'm surprised that they would sell two incompatible parts with the same part number.

 

[mickyg]

hi just noticed from your post that you have the vuw turbomax, not the later turbomax as I previously suspected. There is only the one plate heat exchanger on this model, so ignore my previous info regarding this.

 

[aris]

Right,

I did an X800 treatment on my system and it seems to have solved the problem. In fact, i've never had hotter water come out of this boiler!

The boiler has been in place for about 10 years now and it has mostly had inhibitor in it, but perhaps I didn't flush and replace it _every_ year, but I will certainly do so now.

For anyone else who might search these forums, this is what I did:

I let a bit of the water out of the closed system, then added the X800 cleaner via one of the upstairs radiators using a funnel. I re-pressurised the system, and then started up the CH and let it loop around for about 30 mins, then I put the DHW on, and let that loop through for about 30 mins, and did the same again - a total of 2 hours as the instructions say.

I flushed the system by letting gravity do its work, then by opening the tap to the closed system which (I think) forced water to go throughout the loop and force out any old water in the loop. I noticed that the water was particularly grey - I flushed until it came out clean.

I then re-presurised the system and let it run for about 10 mins, then repeated the above and flushed it all down again (just in case). After that I filled up the system, and added a litre of X100 inhibitor.

Hopefully all will be well for next winter!

My only issue now is that I think I have a faulty DHW microswitch. DHW does not always come on - but when I fiddle with the switch, it suddenly comes on. The manual says you can just replace this - but I see it is attached to the diverter valve. Is it easy to swap out?

 

[kevplumb]

yup as long as the diaphram in the diverter is ok and the white plastic arm is not about to fall apart (and they do )