Gas fire flue(redundant)

[caseyjones1961]

Hi all, l had an old(80's) gas fire removed from my bungalow, it had a brick flue that ran up about 8ft through the wall cavity, into the loft space leading to a ridge vent.
The fire was replaced with a new fanned flue item that vents through the external wall only.
All has been ok but recently l have a small damp patch on the internal wall below where the old flue ends.
No indication of ingress of rain on the external wall so l'm thinking that with heavy downpours the rain is getting in through the ridge vent and making it's way down the flue and dripping out the bottom.
Is this likely to be the case?
The gas fire installer didn't want to get involved with the old flue because of the risk of it being asbestos, he said it would be fine if left undisturbed in situ.
l have someone quoting to remove the ridge vent and replace it with standard ridge tiles but have concerns re condensation building up in the redundant flue.
If the ridge vent is removed but the top of the flue left open inside the loft will that be enough to keep the flue dry/free from condensation?
Any advice much appreciated.

 

[Madrab]

Usually with pre-cast, if it's being left in place, then an air vent top and bottom to allow a bit of circulation will be enough to keep it moisture free. If it's all internal though then it would normally be fine. I would get it looked at and sealed/boxed in if there is an asbestos risk.

 

[caseyjones1961]

Thanks...l can't easily vent the bottom as it is inside the wall cavity, the top is easy enough to do though from inside the loft.The whole length of urastone(asbestos) flue is inside the loft so not much point boxing it in.
I"m wondering if l'm on the right track as l thought the cowl over the roof vent is meant to stop water ingress?

 

[Madrab]

The cowl is exactly for that though of course, in strong winds and rain then water could always be driven into it I guess.

 

[caseyjones1961]

There seems to be quite a large gap under that cowl part and we've had lots of heavy sideways rain recently, clearly not a lot of rain going down if any, as the damp is pretty minimal.
If the old fire had been in situ where would any rain go if it entered the flue?

 

[Madrab]

Most of it would just make the flue wall damp at the top normally