Vaillant aquaPLUS combi (VUI 362-7) - very poor DHW flow.

[jeffwhite]

DHW flow now measured at less than 4 l/min. Should be lot higher. Engineer has changed gas valve (other unrelated problem), removed and de-scaled DHW heat exchanger, changed divertor valve and now OK, removed and checked flow regulator (aqua sensor I believe) and now OK, removed and checked DHW pump and OK also. Incoming mains filter also checked and OK and cold water pressure is fine. The whole system has been flushed and the system pressure is OK at 1.5 or thereabouts. He is scratching is head and I am frustrated, so now I am asking questions on this forum.
Having seen the engineer at work I am interested enough to find the answer for myself.
There is a small internal valve of some kind in an impellor housing in front of the DHW pump - he showed me this. Could this be faulty and restricting flow ?
Are there some adjustments to the gas valve not yet made which is restricting the boiler ?
Are there any other flow restrictors which neither he nor I are aware of?.

Any kind of advice much appreciated. We do have good central heating and some hot water but the poor flow is becoming increasingly frustrating.
Anything useful will be passed on for registered engineer to undertake.

 

[Agile]

I have not been to your model which is surprising as they are a very useful and should have been popular as the current equivalent has been.

For engineers, this is a 36 kW combi with a 15 li store. Obviously the predecessor to the 937.

Your engineer has checked the most obvious components inside the boiler.

But many forget the basic first tests. Your boiler needs a dynamic minimum pressure at the inlet of 0.7 bar and that's a good thing to test as soon as the most likely boiler parts have been checked.

On the later 937 there is a plastic connection to the store vessel which can collapse and cause your symptoms. There was a posting here within the last six months which you could search for and show to your engineer.

Tony Glazier

 

[jeffwhite]

Many thanks for your speedy reply. Much appreciated.
Luckily I am covered by service agreements and I hope I will not have to spend much on this issue, but before I call the engineer back, I have looked inside the casing for the part you have described. (I am sure just looking won't harm anyone !!). I think I can see the DHW expansion vessel (part no. 181081 which I got from the manual) which is right at the back of all the pipes and wires. It is a ball like structure and there is a connecting tube to one end and a valve at the other end, but no sign of any plastic connections.
The pressure showing on the front of the boiler (is this what you meant by dynamic pressure ?) still holds steady at about 1.5 bar.
Also, for what it is worth, the pressure coming out of the hot tap looks simply like gravity pressure (my boiler is in the loft).
He did carry out incoming gas pressure tests which were fine. is this the manometer device being used?
Apart from frustration, I am fascinated by things like this and have a need to 'understand' what is going on.
I will wait for further responses from yourself or anywhere else before I call him back. He has already spent a lot of time here in the loft and draining the system down is a messy, time consuming business.

 

[Bunnyman]

Dip tubes collapsed right bastard especially in loft, probably only vaillant fixed price repair to sort this, not many will try it

 

[Dan Robinson]

Let's be honest. Only Vaillant could afford to do this.

But there would be another honest independent robbed by poor design.

 

[Bunnyman]

Get back in the chamber gash boy

 

[bell824]

Let's be honest. Only Vaillant could afford to do this.

, actually for the part price if you had the world of knwoledge then you could do this very well and still make a decent buck pain in the arse job but two hours labour charge and she would be as good as new

 

[bazdaman]

Get back in the chamber gash boy

Best post ive read all day!

 

[Agile]

Many thanks for your speedy reply. Much appreciated.

Luckily I am covered by service agreements and I hope I will not have to spend much on this issue, but before I call the engineer back, I have looked inside the casing for the part you have described. (I am sure just looking won't harm anyone !!). I think I can see the DHW expansion vessel (part no. 181081 which I got from the manual) which is right at the back of all the pipes and wires. It is a ball like structure and there is a connecting tube to one end and a valve at the other end, but no sign of any plastic connections.

You may be sure! But unfortunately you are wrong.

The case you think is safe to open is actually the sealed combustion casing which only a gas reg engineer should be opening.

Only the mains water side of the boiler needs draining which is not messy because its clean water.

If you have a maintenance contract then dont be sorry for the engineer thats the service you are paying for.

Of course they dont pay so much and only get less capable engineers. Thats why we know what it is likely to be and he does not!

Silly thing if he was more capable at diagnosing faults then he would do it quicker on the first visit!

Tony

 

[jeffwhite]

Thanks to all who have an interest in my post.
As it is now Bank Holiday, I will be unable to progress this with the engineer until later in the week, but as previously explained, at least I have full CH and HW (albeit very slow).
Apologies to 'Agile' - I gave the wrong name to the part I thought he was describing. I am still 'just looking' in the boiler and I can see just the lower portion of the store vessel (15 litres - Vaillant part no. 064072 - again seen from the manual). There are two connections going in at the bottom - right hand one appears to be the outlet to the DHW going downstairs - the left hand one comes from the DHW heat exchanger- so I guess this is the feed to the store vessel. Both connections are copper fittings.
I am not qualified to go further and will be leaving this work to the right people, but I would like to know (and understand) what these dip tubes are - are they internal to the store vessel ? can they simply be removed and replaced from underneath ? Is there more than one or two ? What is their purpose? does the problem mean replacement of the entire 15 litre store vessel?.Is the slow DHW problem definitely as a result of these faulty dip tubes?
I guess I am really asking these questions in order to be confident about what I am going to be discussing this week with the engineer.

 

[Bunnyman]

If you have a proper engineer u dont discuss anything ! I would be insulted an walk away if a customer started tellin me my job, just pay the fixed price on this occasion an stop dancing round the problem,

 

[jeffwhite]

Just thought I would round off this topic as all is now well. Thank you to 'agile' for alerting my engineer to the possibility of those tubes inside the 15litre storage vessel. He had not seen this problem before.
A good 4 hours however and a lot of mild swearing later, the vessel was removed (the vessel appears to be removed from the top of the boiler and there is limited headroom in the loft) and I was shown a plastic green tube internal to the vessel which was clearly perished( the upper 75% of it was simply crumbling away) .
My hot water flow appears to be back to normal, and I seem to have had the added benefit of almost everything else inside the boiler having been renewed or overhauled. I am told this may well give us another 5 years out of the system.
A result, so thanks again to all and I hope anyone else with these symptoms sees this topic just in case it is the same fault.
Incidentally, I helped a lot during the works ( fetching and carrying up and down a loft ladder was appreciated by him) and at no time did I interfere or try to tell him his job - just the opposite he was glad to see me interested and of course taking the trouble with these posts).