Vaillant Thermocompact diagnosis

[bertiebooth]

Please help me. I've read everything I can find on this web site and haven't found the answer.

I have a Vaillant VC GB 242 EH, and I think it has several faults.

I called Vaillant today because I discovered that the boiler kept lighting even during the off periods for heating and hot water. Vaillant concluded that the main PCB has a fault, so I'm arranging for a replacement.

The next problem is that it appears to be overheating - after a few seconds of being lit it makes disturbing whooshing and boiling and bubbling and clanking noises.

To me this means that water isn't being drawn from the boiler quickly enough or the heat isn't being transferred into the water quickly enough, such that there are hot spots inside the heat exchanger where water is literally boiling.

Apart from a possible blockage, or a pump problem, the boiler seems not to be able to detect that it's overheating, judging from the fact that the overheat device doesn't operate.

So I think the following components are all suspect:

1. Pump
2. Overheat sensor.
3. Overheat cut-out device.
4. Heat exchanger.

I've taken the pump apart and the impeller is firmly attached, and the spindle turns when it's supposed to.

I've measured the resistance of the CH thermostat, which is zero Ohms, and the NTC resistor on the flow pipe, which is 2K Ohms.

Is there a way of testing the overheat sensor and cut-out device?

Is there a way of determining whether or not the heat exchanger is scaled up, or blocked, or both?

Is there anything else I should be looking at?

 

[MrGassafe]

Your boiler is in a dangerous condition.
vailliants are among the worst boilers there are and you should get it removed as quick as possible.
Dont mess about with it but replace it soon or you you could get killed.

You should look at atmos, viessman, broag. Even a ideal is better than these bucket of co producing rubbish.

 

[45yearsagasman]

Your boiler is in a dangerous condition.
vailliants are among the worst boilers there are and you should get it removed as quick as possible.
Dont mess about with it but replace it soon or you you could get killed.

What an absolute load of C**p. Vaillant boilers,even ones of this vintage give many years of good service but a lot of so called gas engineers do not understand how they work.It is plain that this one has a couple of issues but is not beyond repair.Difficult to diagnose without being in front of boiler,but a good Vaillant engineer should be able to sort it out.

 

[DP]

Pump is unlikely to be faulty as not only does it pump water through the ‘zone’ that needs heat, it also provides ‘power’ to position the boiler components to carry out required functions. So, if pump was weak or duff, burner unlikely to ignite.

“Your boiler is in a dangerous condition.
vailliants are among the worst boilers there are and you should get it removed as quick as possible.
Dont mess about with it but replace it soon or you you could get killed.

You should look at atmos, viessman, broag. Even a ideal is better than these bucket of co producing rubbish.”

Do not know how MrGassafe has come to this conclusion. Can MrGassafe give more information why he considers the boiler to be dangerous, Vaillant being the pits, suggests the boiler should be removed as a matter of urgency and feels this is a killer boiler. MrGassafe, where did you get the Co producing rubbish idea from. Are you familiar with this Vaillant model?

OP, great boiler. Get someone in who knows this boiler. 242’s predecessor, the Sine 18 is now approaching 30 years on average. Even that boiler keeps providing good service. When I went on Vaillant 242 course, the only complaint from those attending was that the boiler was difficult to repair as it seldom broke down. What knowledge one had taken on board about the boiler was forgotten by the time this boiler broke down.

My advise to you would be keep the boiler, have it looked at by someone other than MrGassafe (me thinks he does not know this boiler or is simply a boiler changer) and avoid the boiler changing brigade. Should you decide that you want to replace the boiler, do get to know the product and go for it.

This forum is visited by host of posters ranging from those who-have forgotten-more-than-I-will-ever-know to others who have little knowledge but a loud voice

ARGI with GSR

What is this going to achieve? May make the poster look good but those that are good do not need to advertise with silly footnote

 

[bertiebooth]

Thanks to you all for taking the tine to reply.

I can plainly see that my boiler is far from rubbish, in design and construction, reliability and longevity.

With the exception of overheat detection, all of the safety systems appear to be in place and functioning, so I'm going to continue with fault-finding this weekend, partly out of an engineering curiosity.

If anyone could answer the questions I asked it would help me make faster progress.

 

[kevplumb]

Your boiler is in a dangerous condition.
vailliants are among the worst boilers there are and you should get it removed as quick as possible.
Dont mess about with it but replace it soon or you you could get killed.

You should look at atmos, viessman, broag. Even a ideal is better than these bucket of co producing rubbish.

what a clown

 

[Bunnyman]

The vc an vcw r excellent boilers that other blokes a muppet. First check turn power off to boiler remove wire from terminal 4 tape up the wire as it's 240v!! Turn power back on if boiler still fires it's a boiler fault if it don't it's external fault ie stuck motorised valve faulty clock etc.. It won't be a faulty overheat as there r 2 the first is a 97deg stat which switches electrics an pops the black button on the front the other is a 100deg mechanical stat which has a probe into the main ht exch an a manual reset on the black box at the rhs behind the pump

Untitled

• Bunnyman
• 26 Mar 2010
• 499

 

[twgas]

this statement

I discovered that the boiler kept lighting even during the off periods for heating and hot water.

would make me look, to start with at least, at the water section - it may be stuck in the "tap on" position.

 

[Andygasman2010]

Your boiler is in a dangerous condition.
vailliants are among the worst boilers there are and you should get it removed as quick as possible.
Dont mess about with it but replace it soon or you you could get killed.

You should look at atmos, viessman, broag. Even a ideal is better than these bucket of co producing rubbish.

Ha! This has got to be a wind-up... At least I hope it is otherwise that guy has issues!

OP, these boilers are amongst the best ever made so stick with fixing this one rather than getting someone in that wants to change it because he can't fix it. Take heed of bunnyman's advice!

 

[Andygasman2010]

this statement

I discovered that the boiler kept lighting even during the off periods for heating and hot water.

would make me look, to start with at least, at the water section - it may be stuck in the "tap on" position.

Being a VC and not a VCW it's a system boiler so doesn't have a water section.

Going by memory so correct me if i'm wrong!

 

[Happyplumber]

Your boiler is in a dangerous condition.
vailliants are among the worst boilers there are and you should get it removed as quick as possible.
Dont mess about with it but replace it soon or you you could get killed.

You should look at atmos, viessman, broag. Even a ideal is better than these bucket of co producing rubbish.[/quote

I think TRADING STANDARDS should be called in ,this geezer calling himself MRGASSAFE,sounds like missuse of registered trademark!!!!

Numpty

Probably another 6 week course wonder



There is reason why Vaillant are one of the largest suppliers of boilers in UK and definetly isn't the nonsense this geeeza is spouting

 

[twgas]

this statement

I discovered that the boiler kept lighting even during the off periods for heating and hot water.

would make me look, to start with at least, at the water section - it may be stuck in the "tap on" position.

Being a VC and not a VCW it's a system boiler so doesn't have a water section.

Going by memory so correct me if i'm wrong!

oops! I see 'W's everywhere I look, (does that excuse me)

 

[bertiebooth]

Thanks to everyone for your replies.

Please note that is a heat only boiler - one heat exchanger, no divertor valve.

Thank you bunnyman for your fault-finding advice, but I had already determined that the main PCB is faulty.

My focus is on the systems that prevent the condition of overheating. I'm familiar with combustion engine design, so I don't expect to have difficulty understanding the technology used here, but I can't find a description of the systems anywhere.

How do I test the three sensors that control the temperature?
For example, should the boiler modulate the gas flow as the NTC resistance decreases? Is 2K Ohms a reasonable value at room temperature? And should the flame be out entirely before the flow temperature reaches 97 deg. C?

 

[plumb46]

the boiler is firing when not in use because it has a prewarm feature so even if your not asking for hot water every so often it will fire to ensure the secondary heat exchanger is hot so when you draw off the hot water you dont have to wait for it to warm up
the boiling noise you are getting is probably due the to the heat exchanger being partially blocked this can be sorted with a powerflush and replacing the secondary heat exchanger and keep the original and descale it for when it happens again

 

[Happyplumber]

Oh dear oh dear plumb ..........................