Puma 80 DHW problem

[ChrisR]

CLick onthe name in the view which gives all the postings in the plummin section. Email addy is in profile.

I'm not in a really hard water area but your symptom can come in som e combis from scale buildup in tap water side of heat exchanger. I guess yours could be due to that, though the tap water gets heated in the main h/e instead of the more common separate one.

Any comments JV?

 

[Baxi-Remeha]

if flames modulating up and down, its the thermistor, if it was scale, the boiler would be working at full and you would just get a constant temp of water. ie the water wouldnt get hot enough for the thermistor to tell the the boiler to modulate down.....

i think that makes sense.....

 

[Softus]

Hi Jason

The flames don't change at all, even when the CH starts up.

I've discovered a few more things:

1. If I open a hot tap but not enough to trigger the DHW flow switch, then I get nice hot water from the tap (albeit slowly of course).

2. The 15mm stainless pipe that comes from the top of the diverter valve is stone cold - this is the "feed" to the DHW heat exchanger, and I believe that it's supposed to be quite warm, not cold.

3. The DV was new about one year ago, and cured a fault with the CH not heating up (i.e. the reverse of the current problem).

4. There is no draw-off cock in the entire system; and the owner just looked blank when I asked when the system was last cleaned and de-sludged, and equally blank when I asked if the system contained an inhibitor.

Does this lead you to any firm conclusions?

Regards
Winston

 

[ChrisR]

You could try swapping the temp sensors over.

 

[Softus]

Latest news, in case it helps anybody...

I spoke to Potterton, who were helpful, and concluded with *reasonable* certainty that the diverter valve is faulty. This was based on the observation that every other component seems to be doing its job, but the primary hot water is NOT being diverted to the secondary heat exchanger.

Potterton also said that the wax capsule assembly might be the culprit, and that these are available separately; however they are not.

I've drained the system now, fitted a new DOC, injected some Fernox restorer, refilled and tested, and am leaving it a few days. Next step is to get a CORGI to replace the DV. I'll post the results here.

W.

 

[ChrisR]

You could test the resistance of the sensor. I posted the values here recently but have forgotten. Several kOhms cold and 1k at boiling iirc.

As above, the hw and ch sensors are the same, swap them!

The wax capsules ARE available, but don't cost a lot less than a whole DV.

 

[Softus]

Thanks Chris - you've been a great help.

I had forgotten to add that I swapped the sensors, and the behaviour was the same. I also tested the resistance before talking to Potterton and they confirmed that the values (which are on the inside of the casing and also on the PartsCenter web site) were within spec.

I decided the system really needed cleaning out when I heard that the existing DV was new one year ago, so I'll forge ahead with a new DV and that will either cure the problem or eliminate the DV as a possible cause.

Cheers
W.

 

[ChrisR]

Where on the Partscenter websiite does it give sensor resistance values ?

 

[Softus]

Chris,

Sorry about the delay in replying...

The resistance values are shown on the fault finding chart inside the casing.

This chart is included section 6 (fault finding) of the installation instructions document (pages 38-40), which is downloadable from the PartsCenter web site.

Cheers
W

 

[ChrisR]

I've never found any instructions downloadable from the Partscenter web site. Are you SURE ?!

 

[Softus]

Chris

Er, apologies for the confusion. You're quite right of course - I mean to write Parts Arena, not Parts Center. The information is in the Data Library.

W.

 

[ChrisR]

Okey doke, found partsarena.com, where's the data library?!

 

[Softus]

Try this:

http://www.partsarena.com/baxi

and if that doesn't do it for you, then this:

http://www.partsarena.com/baxi/Splash/Splash.htm

 

[Softus]

Oh, and while you're browsing, you might like to try this:

http://www.virtualbartender.beer.com/beer_usa.htm

 

[Softus]

Chris

With a fully working DV the problem is still there.

A further consultation with Potterton concluded that Mr. CORGI needs to return to check the burner pressure. If that turns out to be OK, then they believe the only remaining possibility is that the secondary heat exchanger is scaled. They said that it's possible for a small layer of scale to interfere with heat transference without any noticeable affect on the flow rate.

Does this make sense?

w.