Heat Line VISO 24 DHW Issue

[StevenJames125]

Why thank you Paul

I'm just trying to learn - and have never heard of that one before that's why I asked. I'd have checked the DHW thermistor as mentioned by another poster first - as well as the flow switch was working properley when a demand was made/water runs cold - then there's the case of gas valve high and low settings and of course blocked plate heat exchanger

 

[MACE1]

Using a watch and marked level on a bucket I got the flow rate to approx 9l/m
Set to DHW only, max setting, the boiler burner looks ok and after about 60 seconds you get warm water at about 30 degrees it then trails off in about 30 seconds to 20ish then back again in another 30secs to about 30 degrees. Continues to pulse like that. No audible difference from this fairly quiet boiler.
I am a very practical and pragmatic DIYer but I simply dont know much about boilers as they dont really figure in my day to day.

 

[kevplumb]

Is this to check the plate heat exchanger is partially blocked up Agile? ...

right

now is when you jump in with the suggestion

 

[Slugbabydotcom]

If it was a thermistor issue I think we would have no hot anything or too hot so need urgent advice to get this working before the cold weather bites !

These usually fail safe so you usually get lukewarm water!

Best advice is to check out that thermistor because that is the most common cause of this type of problem.
You could play about getting a reading of the resistance if you want. Its a PITA

JUST FOR TESTING!
I would just disconnect the DHW thermistor wire from the thermistor and the boiler will run safely while you run some water test it on the primary thermistor .... We know this is ok because your heating works fine.
If you get hotter water then that points to the DHW thermistor
Don't be tempted to leave it like that as you have temporarily taken out a line of defence against scalding.

Then get an RGI out to fit a new one


Also check that no one has knocked the gas valve [ECV] partially closed as a restriction in the gas supply can cause the problem.
Many a time I have been called to similar problems to find that someone has thrown something into the gas cupboard and knocked the valve.

Quite often DIYers get their hands on these boilers because they can be bought in B&Q, then they expect it to work on an undersized gas pipe. You need a good flow of gas to heat that water as it passes through the boiler. Much more than for heating.

I wouldn't have thought the flow sensor was at the root of it because the boiler wouldn't fire if that didn't work.

Yes there's other causes but start with the common and the easy stuff

Ive never seen a blocked plate heat exchanger on one of these yet. There's a filter on the return that would block up long before that did

ye god's it's alive icon_razz.gif icon_razz.gif

must be dark icon_lol.gif

Yes Kev m8 I am truly nocturnal again

PS If you want to see a better copy of the MI's with a full display of the fault finding look up Glow worm betacom C .... its the same boiler with a different frock

 

[Agile]

I wouldn't have thought the flow sensor was at the root of it because the boiler wouldn't fire if that didn't work.

Ive never seen a blocked plate heat exchanger on one of these yet. There's a filter on the return that would block up long before that did

I thought if you disconnected the SHW NTC thye stayed off and flash a light?

I go to clean a plate on one every month or so. I have often wondered how they get blocked when there is a filter on the return. I have concluded that its caused by those who drain boilers through the PRV but there may be other reasons as well. All I can say is that blocked plates are very common in my experience.

Tony

 

[Slugbabydotcom]

I thought if you disconnected the SHW NTC thye stayed off and flash a light?

I go to clean a plate on one every month or so. I have often wondered how they get blocked when there is a filter on the return. I have concluded that its caused by those who drain boilers through the PRV but there may be other reasons as well. All I can say is that blocked plates are very common in my experience.

Tony

Read as DHW ntc ^^^

The majority of calls I get for these is for the DHW thermistor

One of us is right. Whatever hes got nothing to lose by trying.
I've been out of the game a bit lately since getting arthritis but as I recall it used to work for me in most cases. I'll concede it might be better to try a new thermistor on the end of the wire just to test it then.

You must be in a blocked PHE blackspot Tony. I haven't seen one for ages.
Maybe we have a better class of cowboy fitters up here

 

[MACE1]

I downloaded the PDF version quite easily however on examination it is obvious there are bits missing. The Map of numbered parts on the boiler has no key for the first half dozen items and many of the later charts are only printed on the left hand side, the right being blank.
I have been unable to identify many of the items discussed above.

(The gas supply is 22mm Copper and the valve is fully on.)

I think following the initial service advice in the manual is my first port of call. Thereafter I need to identify the thermistor in question and take it from there.
It looks difficult to take off the side housing to get to the rear components ! Might this be a case of taking the boiler off the wall to service it ??

 

[MACE1]

I noted when I drained down the system for decorating this summer that the water was a thick light brown colour, similar to rust. On the boiler it says it was 'flushed' about 2 years ago.
It may have had an additive in the water, 'fernox' or similar to give this colour. I know there was a problem before I drained it down.

Could this be a cause for blockages/thermistor/filter ?
Should I be putting an additive into the system and if yes what and HOW do you get it into this closed loop - Inject somehow into the topmost radiator ??

 

[Agile]

The majority of calls I get for these is for the DHW thermistor

You must be in a blocked PHE blackspot Tony. I haven't seen one for ages.

Maybe we have a better class of cowboy fitters up here

But you did not confirm my recollection that an o/c NTC gave a flashing light.

I have been to more stuck flow turbines on these than blocked plates.

Most calls now are blocked plates. I alwas advise cleaning but the landlords never agree and call me again a year later.

Because they are so cheap and sold in Selco they are the choice of builders for landlords. They dont do cleaning in East Europe.

Tony