worcester cdi 28 - heating ok but hot water keeps cuting out

[helpfleming]

I am currently having some building work at home, extending my property. I have retained my existing boiler but the plumber had to extend the flue by approx 2.5m to exit the new lean to roof. It would be worth noting, before any work was undertaken the boiler worked fine.

Now nearing the end of the works I have been dealing with the heating working fine, but the hot water cutting out when used - the tap LED flashs red and cuts off the hot. The 'thermacoupla' has been replaced but the problem still persists... I have lost all faith with this plumber who has admitted he is not sure why it is cutting out but thinks it may be the heat exchanger? (I have read that this can get dirty and stop working but not sure if it relates to my problem?) I am not a money tree and the approach my plumber has it could cost me a fair whack.....I could do we some help ..... any ideas??? and thanks in advance....

 

[ChrisR]

Is your "plumber" Corgi reg'd??
Your boiler does not have a "thermacoupla" or anything like it!
He's out of his depth, and you're paying for his floundering.

 

[bengasman]

Indeed. You either misunderstood your plumber or he is a fraud.
What exactly do you mean by: cutting out?

 

[superdupergasman]

You need to also check the total over all flue length....sounds like it also may be past the maximum permissable from this appliance....
I would stab a guess at most worcesters being 2.4m maximum, unless a new condensing effort with a 5 inch flue.

 

[plumgas]

I think the horizontal max flue length is 3 m on the cdi 28. How long dose it take to switch off/ how fast is the light flashing and do you have to reset each time

 

[helpfleming]

Thanks all, I've done some digging (spoke to worestor technical department) and found out the following:

1. The max flue run for my configuration is 3.0m (mine may be slightly over this.

2. The red (tap) LED light flashes quickly, that is a sympton of an air fault.

3. The air inlet at head of flue pipe needs to be checked along with all of flue to check for blockages etc...

4. If the combustion cover is removed and the red light stays on, then this shows the fault is an air starvation issue.

5. Check if restriction rings have been removed.

6. If all above ok, then it could be the fan....

The plumber is apparently corgi registered, but I am amazed he has not had the approach that if he is not sure what the problem is then ask some one who does!!!

The part replaced was apparently the domestic hot water thermistor - but worestor said this is nothing to do with the problem....

Does the above sound accurate to you guys?

I think a new plumber is required - he should be telling me the above not vise-versa. But I seem to be making progress.....

 

[Agile]

All that is only what is to be expected if the maximum flue length has been exceeded!

The 3 m is of straight flue but not counting the bend on top of the boiler. And further bends are calculated at about 0.9 m each!

The fault is indicative of a flue which is too long! Your plumber should have checked the maximum allowed BEFORE extending it!

It would not be correct but could probably be made to work by readjusting the APS but the manufacturers would not support that because they have fears of condensation in a flue over 3 m long.

Tony

 

[helpfleming]

Thanks Tony -

Forgive my ignorance but what does APS stand for?

Also, when you say further bends are 0.9m each - how is this mean't?

To clarify - the flue exits the top of the boiler, elbows 90 to go through the wall, then after approx 400mm elbows right running horizontally for approx 1500mm, then elbows up to run vertically for approx 1500mm to run through the lean to roof. The cap / inlet is at the head of this vertical pipe. Total flue length approx 3.4m.

Sorry to sound ignorant, but I need to be sure of the issue , to know how to approach this with my plumber, and not be flogged off with some half wit excuse again..

Cheers J

 

[Agile]

Each flue elbow has to be counted as if it were 0.9 m of flue length.

I calculate your effective length is actually 5.2 m !!! Seriously more than 3.0 m

You also raise another issue! Your description shows the last part being vertical! Is that a proper vertical flue terminal or has the horizontal terminal just been made vertical?

Tony

 

[helpfleming]

Tony,

The vertical flue pipe is correct I believe, it is definitely not a horizontal terminal.

So, if effective length is 5.2m will your earlier suggestion of adjusting the APS help?

Regards

J