Ferroli Modena Boiler Conundrum

[chuckalicious]

Right. Got a complete fud of a problem and looking for some ideas.

I have a Ferroli Modena 102 combi which has concentric flue.

When we bought the house, the boiler was cutting out when running hot water. Had a firm out who said the fan needed replaced. After the fan was replaced, which was maybe 18 months ago, the issue seemed to be sorted.

However it has always sounded a bit "chuffy" in that it sounds like it is trying to pull air in. It was due a service and a friend is a boiler engineer so asked if he could take a look. The seal on the combustion chamber had broken away at one point which would have allowed air to be sucked in plus a gasket on part of the flue was misformed. He replaced both of those with new Ferroli parts and after putting the case back on it started making a very strong shaking sound. Cracking the case open stopped it and it was clear air was being pulled in through the open case.

The fan has been removed and it runs perfectly smoothly.

So he has checked the flue, which is within the 4m max vertical length, the part that comes out the roof also seems fine. The flue I think is 4" diameter (or if not it is what the Ferroli manual states is right).

It is clearly an airflow problem but he cannot see why, short of replacing the flue with a 5" one.

Makes me wonder if this has always been a problem with the boiler and the previous owner found that removing a bit of the seal worked, or just loosened the case a bit to let enough air in.

Short of replacing the flue, any ideas that we could try? Don't want to waste any more of my mates time!

Cheers.

 

[ianmcd]

is there a restrictor disc fitted in the flue outlet ?

 

[chuckalicious]

is there a restrictor disc fitted in the flue outlet ?

Nope, no restrictor that he can see. Sorry I forgot to mention he had hoped it was a restrictor.

 

[ianmcd]

are you measuring the flue total length from the flue terminal to the boiler ? are there any bends ?

 

[chuckalicious]

Yup, from terminal to out the roof. No bends.

 

[chuckalicious]

Or sorry from boiler terminal to roof. Just to be clear

 

[chuckalicious]

This isn't considered a reducer is it? This was the old connector from the boiler to the internal pipe in the flue. Had to order a new one for a new gasket.

 

[ianmcd]

No that is the correct fitting for a vertical flue and the flue as you correctly say can be 4M from there to the terminal if no bends, if a restrictor is fitted it will be on the outlet before that fitting is attached, sadly you have a boiler that is very sensitive to air differentials, really sounds like a flue restrictor is still in place to be honest

 

[chuckalicious]

Cool. There is definitely nothing else there then - he had a really good look and the coupler or whatever you call it was replaced too as the gasket on that was shot.

Had a look down the flue from above and nothing in the way either.

 

[cross thread]

has the venturi been replaced very week point

 

[chuckalicious]

has the venturi been replaced very week point

Is the Venturi the fan? This was replaced about 18 months ago.

 

[cross thread]

in the fan 2 seperate parts they become brittle

 

[chuckalicious]

Ah right. Would need to look at that. Certainly the fan is running super smoothly. With the case open the draw of air turns the fan and when running the boiler with the case off you can see the fan running nice and smooth and silent. It's only when the case goes back on that it gets bad.