Problems of a flue that's too long

StuB · 13 Nov 2006

Hi All,

Can someone tell me what the likely problems would be if a flue is longer than the manufacturers maximum stated length other than a voided warranty?

The boiler in question is a Worcester Bosch 35CDI. I'm guessing that it may not be able to get enough air to or from the boiler. Presumably this would only be evident on full load?

Would a boiler run 'rich' on full load if it can't get enough air or is it like a car where it only inserts as much gas as there is air to go with it?

Cheers

Stu

simond · 13 Nov 2006

Well, for a start the APS might not make, causing the boiler not to start.

Worcester make a 125mm flue for situations where the 100mm might not extend long enough, I assume you have looked at this option?

Goes without saying that knowingly connecting a gas appliance where the flue - which is the most critical piece of safety related equipment - is not to manufacturers instructions, would be extremely unwise from both a safety and prison perspective.

Would add that you are clearly not experienced with gas or you would be aware that a combi runs flat out when there is a HW demand.

StuB · 13 Nov 2006

Hi Simon,

Thanks for the reply.

I rightly agree with you that only a competent person should install the a boiler and I don't claim to be one hence my reason for employing a CORGI engineer to do it. It's a shame that it's me having to double check his work as I don't think it's up to standard and in line with manufacturers specs and regs.

You may of read on another thread the guy has installed a 35 CDi II RSF instead of a 35 CDi this is what made me start checking other things. I'm basically gathering together a list of the faults that I think he has made and I'm going to tell him to get it sorted or more likely to go away and I'll get someone else to. I just like to understand the ins and outs so when he says that's not a problem I can say yes it is because .....

I think the flue is about 0.8m too long which I'm guessing is significant.

I did know that the HW on full is the largest heating requirement for a combi and I'd like to know does the boiler just provide more gas to burn assuming that there should be enough air to go with it or does it just add gas upto the amount of air available?

I'd guess at the former so does that mean that if it can't get enough gas it is going to run rich and therefore less efficiently?

A 125mm flue is what I'm looking at but it's going to be more difficult than the 100mm one fitted due to space restraints.

Thanks for the help.

Cheers

Stu

simond · 13 Nov 2006

You have an old WB unit which is not condensing. The gas/air mix is critical to the safe working of the appliance and you can rest assured that WB give the maximum tested safe flue distance in their book.

If this is exceeded then it needs to be addressed. Quite what happens if the flue distance is exceeded rather depends on a number of parameters; you could have incomplete combustion, the boiler could be subject to external pressure variations causing blow out, the list goes on.

The 125mm flue option is your only one, by the sound of it.

arfurrrr · 13 Nov 2006

hey up stuB , I wouldn`t pay the guy , sounds like he is a right dodgy git . who has no idea of the regs .

have you said anything about the boiler been non condensing yet ?

arf

StuB · 13 Nov 2006

simond said:
You have an old WB unit which is not condensing. The gas/air mix is critical to the safe working of the appliance and you can rest assured that WB give the maximum tested safe flue distance in their book.

If this is exceeded then it needs to be addressed. Quite what happens if the flue distance is exceeded rather depends on a number of parameters; you could have incomplete combustion, the boiler could be subject to external pressure variations causing blow out, the list goes on.

The 125mm flue option is your only one, by the sound of it.

Thanks for that Simon, gives me a few reasons to say back to him when he says it's not a problem and 'there's plenty of leeway built into those figures'.

StuB · 13 Nov 2006

Hi Arf,

As mentioned the other day we've already part paid for the job which included a number of other things as well as the boiler which have been done satisfactorily and we still owe about £1300 and I'm withholding that until it's all sorted.

I have spoken to him briefly and have said I'm not happy with the situation but I haven't yet got a resolution from him as he was 'busy' when I spoke. I'm going to try and speak to him tomorrow to try and find out what he intends to do and failing that find someone else.

He's basically trying to lay the blame on me saying that I asked for a 35CDi (which I did) and that's what he fitted (a 35CDi II RSF) but surely the whole point of getting a CORGI guy in is so they know the rules of what should and shouldn't be done and that you shouldn't be fitting a non condensing boiler.

Cheers

Stu

arfurrrr said:
hey up stuB , I wouldn`t pay the guy , sounds like he is a right dodgy git . who has no idea of the regs .

have you said anything about the boiler been non condensing yet ?

arf

Agile · 13 Nov 2006

Can we try to consider the situation in perspective please?

Have you checked to see if he really is registered by checking his reg no at corgi-gas web site for example? He sounds dogey to me!

Firstly when you asked for a non condensing boiler did he tell you that a condensing boiler is required?

Has he notified the boiler to CORGI as he is required to do IF he is registered? Ask him about this !

There is a VERY powerful tool available to you if he is registered ! You can report him to CORGI and they will inspect and send him a defects notice and require him to put it right at his own expense within 20 days !!!

Your boiler provides a known amount of gas and assumes there is enough air to burn it fully at full power. Generally the APS will not operate if there is insufficient air.

If the flue exceeds the maximum length the first most likely problem is condensation and thence corrosion!

Tony

StuB · 14 Nov 2006

Hi Tony,

Yep I called CORGI when I first contacted him re a quote and also last week to recheck his name and company name against their database and he is registered as being suitable for gas and central heating work.

I first asked for a combi boiler with my only real requirements being a decent make and to be a larger one capable of a higher flow rate, I gave the figure of 14l/m which I gained from speaking to friends and from threads on here. He turned up with a 25CDI (not sure if this was a condensing version or not) and I rejected this saying it's not big enough. He asked what I wanted and I said after looking on the WB site a 35 CDi (I was referring to the Greenstar) should do what I want and he then fetched a 35CDi II RSF. I didn't realise they still made non condensing boilers and that this was different to what I'd asked for.

At no point did he ever tell me it was a non condensing boiler or that they shouldn't fit them.

I presume he hasn't notified CORGI of the install yet as I realised the problem before they finished their work and told them to stop until we sort it out.

Thank you for letting me know about the CORGI inspection, it's nice to know I have something that may make him listen if normal lines of communication fail. I assume if I went this route and he failed to comply it would cause him problems.

Thank you for answering my question re the gas/air ratio.

I'll try and speak to the guy again tomorrow and I'll let you all know the outcome.

Cheers

Stu

Agile said:
Can we try to consider the situation in perspective please?

Have you checked to see if he really is registered by checking his reg no at corgi-gas web site for example? He sounds dogey to me!

Firstly when you asked for a non condensing boiler did he tell you that a condensing boiler is required?

Has he notified the boiler to CORGI as he is required to do IF he is registered? Ask him about this !

There is a VERY powerful tool available to you if he is registered ! You can report him to CORGI and they will inspect and send him a defects notice and require him to put it right at his own expense within 20 days !!!

Your boiler provides a known amount of gas and assumes there is enough air to burn it fully at full power. Generally the APS will not operate if there is insufficient air.

If the flue exceeds the maximum length the first most likely problem is condensation and thence corrosion!

Tony

StuB · 14 Nov 2006

Hi All,

Just spoken to the CORGI guy again at length and basically he's not happy and in his opinion and the property is exempt from needing a condensing boiler and as I asked for and accepted that boiler it's my fault and he won't pay to change it.

I've spoken with CORGI and they say the condensing boiler is a building regs issue but the flue being longer than stated by the manufacturer is their issue and they can get someone to inspect that.

Either way it looks like I've annoyed the bloke and can't see him finishing off the remaining work.

Any advice on how to continue?

Cheers

Stu

doitall · 14 Nov 2006

Not that I think it's the main issue but if you ask the manufacturer they will problably ok the longer flue, depending on location.

There's a new prog coming up on C4 soon, whereas disputes of this kind can be sorted amicably to both parties, I can post the link if you like, but Mods may remove it.

stick an email in your profile.

simond · 14 Nov 2006

I would eat my lunch if Worcester agree to a longer flue tham MIs......

Do tell us how you get on.

doitall · 14 Nov 2006

simond said:
I would eat my lunch if Worcester agree to a longer flue tham MIs......

Do tell us how you get on.

Never been refused an extra 800mm yet from the manufacturers, although not tried Worcester.

Softus · 14 Nov 2006

Agile said:
corgi...He sounds dogey to me!

Agile, you're at you're most witty when it's unintentional. Heck, I could even like you.

Agile · 14 Nov 2006

But you DO like me !

Thats proved by how often you reply to something I have said !

Particularly the humourless wit !

diynot

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Problems of a flue that's too long

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