Ravenheat RSF84 Flue

[stuart_adair]

Afternoon all,

Can you please help me with some advice about the flue on my Ravenheat combi ?

I've had to move the flue from its vertical position to a horizontal outlet which is 3.5m from the boiler. This is just within specifications for the maximum flue length. The problem is that when the boiler fires up the burner lights for about a minute and then starts behaving as if were being starved of oxygen. It cuts out, starts up about 30 secs later and carries on for about another minute when the cycle repeats.

If I disconnect the flue pipe in my loft as a test only then the boiler fires up and burns fine - its only when I connect the extensions that I get a problem.

Does this make sense - If the flue length is too long would the boiler behave this way and is there any sort of adjustment I can make to improve the situaiton.

Thanks in advance for your help.
Stu

 

[gas4you]

Does this 3.5M include 1M for each elbow?

Are all the seals good in the flue connections? Boiler could be sucking in its own exhaust!

 

[stuart_adair]

That might be the issue. I've got 3 90º elbows and I never counted them as distance.

Is there anyway I could get this arrangement working ?

Stu

 

[Rob]

You may be able to increase the flue size to 125mm (5'') to allow greater total length. Will need to check MI.

Or maybe twin flueing?

 

[Slugbabydotcom]

Follow the red tube from the APS to where it connects on to the flue restrictor ring. If this connection is at 0º or 180º to the direction of the flue it doesn't detect the pressure difference as it should. Remove the 4 screws and rotate it to 90º and it usually works.

If it still doesnt work then take the ring out and make sure venturi is clear. Sometimes the flue doesn't fit as concentric as it should in which case you will need to try the ring in different positions until it works.

 

[corgiman]

You are obviously a keen diy'er

But please for the love of goodness do not be tempted to use your appliance with the flue off

recently a chap was imprisoned because he was fitting a boiler for a family and left it working with NO flue

he caused the death of two children and their grandmother

please be careful

 

[Rob]

Follow the red tube from the APS to where it connects on to the flue restrictor ring. If this connection is at 0º or 180º to the direction of the flue it doesn't detect the pressure difference as it should. Remove the 4 screws and rotate it to 90º and it usually works.

If it still doesnt work then take the ring out and make sure venturi is clear. Sometimes the flue doesn't fit as concentric as it should in which case you will need to try the ring in different positions until it works.

Slug, you saying that 3.5m and 3 x 90* elbows is within limits

 

[Slugbabydotcom]

No but if theres any way of making it work then that will do it. I havent looked at the MI to check the effective length situation. I was writing my post when the OP replied with the actual number of bends he had on his new set up and erroneously assumed that it would have been in order.

Edit: Had a look at the manual now. Max effective length is 4m with the following provisos:-

Each extension length extends the pipe by
approximately 1000 mm long up to a maximum
of two extensions.

AND

IMPORTANT: in line flue bend - 750 mm
must be deducted from overall length for
each 90º bend. Obtuse flue bend - 375 mm
must be deducted from overall length for
each 135º bend

Looks like you might have to twin flue it!

 

[stuart_adair]

Ok point noted. I only ran it for a minute though.

Just to let everyone know that I've managed to re-route the flue so it now goes straight up through the roof, works perfectly.

Thank you very much for all your help.

Stu

 

[corgiman]

Ok point noted. I only ran it for a minute though.

Just to let everyone know that I've managed to re-route the flue so it now goes straight up through the roof, works perfectly.

Thank you very much for all your help.

Stu

good luck with the notification as well

 

[Agile]

Did you remember to buy the proper vertical flue terminal ?

You cannot just use the horizontal terminal vertically !!!

Tony

 

[stuart_adair]

Certainly did. I was lucky enough to be given the roof vent free when I bought the boiler.

Stu