Vaillant 831 plus plate heat exchanger replacement - how to?

BG - changed the diverter valve due to leak.

Next day hot water reached 80 then boiler shut down and water went cold . Had to turn the tap off then back on to get a burst of hot water

BG - came back said heat exchanger needed changing and a power flush

Since the boiler and all the rads and pipe work are 4 years old - I didn't believe this. (Fernox inhibitors etc in system)

Asked BG to check the PCB after reading this forums old posts. He said that it was fine.


Got a local GS engineer round , he fitted a salamander mains booster for no reason at all and didn't fix the issue.
He checked the domestic water heat exchanger and said it was fine and the water in the system is fine.

Problem still there next day.

Bought a new heat exchanger , I fitted it last night.
Visually flow tested the new one vs the old one not much difference

Symptoms didn't change with new heat exchanger

Central heating works fine all the the above issues.


Woke up this morning and disconnect and reconnected flow sensor plug.


Now all of a sudden I can have a 10-15min shower no problem.

Haven't attempted a bath yet----which has been a issue since the dv valve was changed.
 
I'm sure nothing I have done has actually rectified the problem - it's just by chance .

I predict in a few days the issue will return and I will try a different GS engineer
 
Hazee said:
Got a local GS engineer round , he fitted a salamander mains booster for no reason at all and didn't fix the issue.
He checked the domestic water heat exchanger and said it was fine and the water in the system is fine.
Click to expand...

So how does this local GS engineer come round and fit something not required and still have nothing to say about why the boiler is not working?

Even more relevant did you pay him for doing nothing useful? If so why?

Tony
 
Hazee said:
Woke up this morning and disconnect and reconnected flow sensor plug.
Click to expand...

The obvious expectation is that there was a poor connection on this plug.

But had that been the fault then a no demand shown for HW would be an obvious fault and lead any engineer to investigate the flow sensor.

Tony
 
No I didn't pay him , and i don't think he will ask for money .

At the time he came round the hot water worked for taps and shower.

But as soon as he ran the bath it would heat up the water and the boiler would shut down.

Think he was abit stumped to what the issue was.

- i still haven't tried to run a bath
 
Since you can walk up to the bath and turn on the HW tap, one wonders why not.

You don't have to undress and get a big towel just to test it!

Tony
 
Hazee said:
No I didn't pay him , and i don't think he will ask for money .
Click to expand...

But what about this Salamander thing?

Did he remove it?

What was his intention in fitting it?

Did he ask you your permission or say what it would do for you?

Tony
 
Ran half a bath seems to be fine.
Temp sticks between 68 - 73c.

I think the basis of thought was that there may have been a issue with water pressure

http://www.salamanderpumps.co.uk/pumps/home-boost/

I asked him to check the exchanger / condition of water etc and try and find the issue.

He changed a few fixing that he thought was restricting the hot water flow to the bath and added the pump. --- admitted it still temperamental and said see how it goes.

Pump is still fitted


Following couple of days the issue of the boiler shutting down due to hot water demand moved to the shower too.


Lost faith with BG and local GS plumber.

Now will see how it goes. Know a good GS plumber but im out of his area - will convince him to come round if any problem persist
 
Water temperature should not exceed 55 C for safety reasons.

Exactly how are you measuring the water temperature?

Tony
 
Hazee said:
Pump is still fitted
Click to expand...

Is the pump fitted to the cold inlet to the boiler?

Did he make any flow rate measurements before/after fitting this pump?

I do hope that he will get paid for this pump! they are quite expensive.

Tony
 
Temperature is the flow temperature on combi gauge - factory is 75 c

Pump makes realistic no difference to flow when it switched on or off . I know it's expensive . I won't be paying for it. He can remove it if he likes

I obviously will pay him for time he spent of changing some fixings.

Im a tradesman and wouldnt be expected to be paid at all if I didn't resolve the issue.
 
Last edited:
Agile said:
Did he make any flow rate measurements before/after fitting this pump?

Tony
Click to expand...


Just tested the tap...

Strongest tap in the kitchen

Pump on 8.6 litre per min

Pump off 6.8 litre per min

I presume without pump would be slightly higher than pump off.
 
I would not expect to fit an expensive pump unless my diagnosis had indicated a benefit to be obtained by having it.

Seems your engineer did not bother to explain to you that the boiler display is actually the circulating primary water. It is NOT the actual hot water temperature. That is about 10-15 C lower!

Tony
 
Agile said:
I would not expect to fit an expensive pump unless my diagnosis had indicated a benefit to be obtained by having it.

Seems your engineer did not bother to explain to you that the boiler display is actually the circulating primary water. It is NOT the actual hot water temperature. That is about 10-15 C lower!

Tony
Click to expand...


Where did I say it was the hot water temp , I've never measured the hot water temperature
 
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