Vaillant VCW GB 242 EH Boiler - Is it Diverter Valve?

[Agile]

From a lay persons view not much else can be wrong. Heat from flame heats the primary HEX which pump then circulates hot water to either secondary HEX or CH. If CH is reasonably ok but not DHW. This must surely mean that something is happening when in DHW mode. Simply that water is not getting heated enough from flame or there's a blockage in the HEX (or diverter not doing its job)or somewhere else in circuit in DHW mode.

Thanks again
Andy

You are back doing what I think is unhelpful to yourself, speculating as to whats wrong.

I appreciate that some people in our trade are quite incompetent and that you have been unfortunate in calling some out to your own boiler. Thats not helped by the common perception that boilers are fixed by "plumbers" and they are all thick and all they are good at doing is ripping people off.

However, some of the best engineers in the country give advice on this forum. We have asked you a lot of questions which you have been slow, reluctant or have not answered at all and instead preferred to willy nilly change parts all to no effect.

Its only possible to diagnose faults by doing tests and measurements.

The stumbling point now seems to be that a thermal survey would be needed to advance the diagnosis. Thats assuming at some point the NTC sensor has been measured as I cannot remember that being mentioned.

Obviously if you are happy to call vaillant then thats something you should have done at the beginning rather than changing so many parts.

It is your boiler at the end of the day!

Tony

 

[trelo]

Andy... you absolutely read my mind about the Y shaped tube to the left of the combustion chamber. I looked at that and thought 'I wonder if your blocked?' I got put off the idea though because that flow pipe gets hot when in CH mode(obviously not in the chamber, at the HEX )...now is that normal? (hot flow in CH mode)

Sorry about the green light confusion... I think i misunderstood your advice about how to check that. The green light seems to be dim and stays that way wether DHW or CH mode. What does the NTC do exactly? What does NTC actually stand for?

 

[Agile]

An NTC is a resistance which reduces when it gets hotter and is used to sense the temperatures at different parts of boilers.

Tony

 

[tamz]

You have said your boiler is 15 years old. Yank it off the wall and get a gas guy to fit a new one and be done with it.
Btw 5 pages of Q&A here that took me 10 mins to read and a week of to-ing and fro-ing to write.
Any decent boiler man would have run all these Q&A's through his head in a shorter time than it has taken to type this reply and gotten further forward! If as you say the gas rate is fine the heat must be going somewhere if not to the water

 

[trelo]

From a lay persons view not much else can be wrong. Heat from flame heats the primary HEX which pump then circulates hot water to either secondary HEX or CH. If CH is reasonably ok but not DHW. This must surely mean that something is happening when in DHW mode. Simply that water is not getting heated enough from flame or there's a blockage in the HEX (or diverter not doing its job)or somewhere else in circuit in DHW mode.

Thanks again
Andy

You are back doing what I think is unhelpful to yourself, speculating as to whats wrong.

I appreciate that some people in our trade are quite incompetent and that you have been unfortunate in calling some out to your own boiler. Thats not helped by the common perception that boilers are fixed by "plumbers" and they are all thick and all they are good at doing is ripping people off.

However, some of the best engineers in the country give advice on this forum. We have asked you a lot of questions which you have been slow, reluctant or have not answered at all and instead preferred to willy nilly change parts all to no effect.

Its only possible to diagnose faults by doing tests and measurements.

The stumbling point now seems to be that a thermal survey would be needed to advance the diagnosis. Thats assuming at some point the NTC sensor has been measured as I cannot remember that being mentioned.

Obviously if you are happy to call vaillant then thats something you should have done at the beginning rather than changing so many parts.

It is your boiler at the end of the day!

Tony

Tony... I'm not happy to call vaillant at all! I actually like doing this stuff...
I've answered most questions you and the others have asked. I had already changed the HEX way before finding this forum because the HEX was always the culprit for this problem in the past.
I came here to ask the question IS IT THE DIVERTER? and went from there. I've only changed the diverter and the water section since coming here which in fact needed changing because both had problems anyway.
I followed the advice about checking flow rate and did basic gas meter check which everyone has said so far seems ok. I've now got to try and do a thermal test as you suggested.
Andy seems to think i should check the Y section in the combustion chamber for blockages which I may do also. He seems to think there could be a modulation issue....
I was starting to think i may be getting out of my depth here which led me to thinking about calling in vaillant... Reluctantly i may have to because i wont mess with gas.
Andy

 

[DP]

Trelo, you have checked and it has been confirmed boiler is using the correct amount of gas.

As has been mentioned, diverter valve rarely fails (I have never had to change a diverter as it is easily serviced) but you have replaced the unit.

The lifting pin that actuates the black cam. I would be reluctant to grease this pin as it is meant to be dry. Have been down that road once but never again as greased pin brings its own problems. If pin fails to travel, replace the bracket that the pin/ shaft travels in.

Have you checked the movement of microswitches on the diverter? Can you post what happens when you ask for central heating and then run hot tap. Remember, correct amount of gas is being used, so heat has to go someplace. What does the temperature gauge indicate when you ask for hot water?

 

[trelo]

Trelo, you have checked and it has been confirmed boiler is using the correct amount of gas.

As has been mentioned, diverter valve rarely fails (I have never had to change a diverter as it is easily serviced) but you have replaced the unit.

The lifting pin that actuates the black cam. I would be reluctant to grease this pin as it is meant to be dry. Have been down that road once but never again as greased pin brings its own problems. If pin fails to travel, replace the bracket that the pin/ shaft travels in.

Have you checked the movement of microswitches on the diverter? Can you post what happens when you ask for central heating and then run hot tap. Remember, correct amount of gas is being used, so heat has to go someplace. What does the temperature gauge indicate when you ask for hot water?

I haven't greased the pin because it was moving freely in its sleeve before the new water valve went in - didn't see the need to. It was the water valve itself that was jammed solid. Servo, switches and cam movement all seem fine when CH or DHW is asked. Diverter is extending and retracting fully now. Old diverter wasn't quite retracting fully. Unfortunately the temperature gauge has never worked. I was told that its reading isn't very reliable anyway (by a vaillant engineer) Thanks

 

[Andygasman2010]

i'm not sure the correct amount of gas is being used.... The green light is dim which you indicated the burner has modulated down.

Check that Y shaped section as described

Pull of the NTC wire and run the hot water, see if that makes a difference

 

[trelo]

i'm not sure the correct amount of gas is being used.... The green light is dim which you indicated the burner has modulated down.

Check that Y shaped section as described

Pull of the NTC wire and run the hot water, see if that makes a difference

Thanks again... Where is the NTC sensor?... diagrams i use online not showing where it is. I thought i'd do this first before cleaning the Y section. What do you think is going on with the dim green light then?

 

[Andygasman2010]

i'm pretty sure the NTC and the Y shapped pipe we're on about are within the combustion chamber, stricktly speaking it's an RGI's job. i can't advise you do that yourself.

The brightness of the green light is proportional to the burner pressure. High burner pressure = bright light and vice-versa. It's only a rough guide though, a propper burner pressure check by an RGI is best.

 

[Agile]

Regardless of how bright he thinks it is, the gas rate indicates that its pretty close to operating on full power input.

The question is where is that heat going to.

With the gas rate measured I would check the DHW flow rate and measure the exact water temperatures inlet/outlet.

Its easy to test if the diverter valve is passing to the rads ( but I dont think thats been specifically confirmed ).

Tony

 

[Andygasman2010]

Given all the checks/test this boiler has had without finding the problem, something must not have neen done right. It's had a diverter valve, water section and apparently the servo valve is ok. Even so, if the diverter wasn't moving over propperly it's unlikely to fire up due one of the diverter microswitch not releasing.

Just trying it with the NTC lead dissconnected will be very good indication of where the fault lies, i wouldn't do anything else before trying that.

If it then works ok, we'll know that the poor hot water is due to the burner modulating down which will narrow the field.

I'm sure i've said this before

 

[Agile]

If it then works ok, we'll know that the poor hot water is due to the burner modulating down which will narrow the field.

But we have been told the gas rate on DHW is about right. So there is no evidence there is any problem caused by modulating down.

Either some information presented to us is incorrect or the heat is not being fully transferred to the DHW. There could be several causes of that.

Tony

 

[Andygasman2010]

It's had a diverter valve, water section and apparently the servo valve is ok

Could it still be passing to the rads?

Just trying to work out what info is most likely to be wrong and what is easiest to check next.

 

[Agile]

Whilst the OP has been very quick to make postings he has been very slow to give us anything presented as being hard evidence of what the appliance is actually doing.

It has crossed my mind that he might possibly have made up some of the evidence just to appease our requests for information?

Tony