Sealing holes around central heating pipes

Hiya

First time posting so apologies if I have posted this to the wrong area...

I'm trying to find the best solution to seal up two holes around radiator pipes that are coming down from the ceiling inside a cupboard (I have a photo but no idea how to post it!)

Calor's engineers left it that way when they installed our LPG central heating system a few years ago, and as we had so much else to do with renovating the house at the time, we just left it. However, I'm now using this room as my home office, and whenever the heating is on I am noticing a foosty loft smell coming down through the holes (plus occasional plaster crumbs and tiny bits of loft insulation, which is annoying).

I've looked around for potential solutions for what I can use to seal around the pipes, but everything seems to have mixed reviews ranging from perfectly fine to catastrophic...

We've looked at pipe collars but don't think they will fit because the two pipes are quite close together and one of them is hard up against the side of one of the holes (also, I'm not sure if they would stay in place hanging upside down from the ceiling?)

A few people have mentioned expanding foam, but the gaps are not that big, and I have a feeling that trying to do that upside down inside a tiny cupboard would probably end in disaster.

I've read that silicone and caulk are not good to use due to corrosion problems.

The other thing I have seen mentioned is flue jointing compound, but not sure if this is safe to use in a room where I will be sitting 8+ hours a day?

Does anyone have any thoughts on what would be the safest and easiest thing to use (I'm guessing it's probably one or the other though!) Any advice would be much appreciated, thanks!

 

I just use low modulus silicon, it remains pretty flexible and wont crack, caulk will crack with heat expansion of the pipes

 

I have previously used this stuff ... https://uk.rs-online.com/web/p/expa...DRhMHO9fePU9_XyDy3RoC9_EQAvD_BwE&gclsrc=aw.ds for closing gaps. Very effective.

 

@ianmcd - thanks, I hadn't realised there were so many different types of silicone! Looks like the neutral stuff is what I would need for using on copper.

When I'm looking online most of the low modulus silicone I'm seeing says it's for exterior use - does this mean it shouldn't be used indoors, or just that it's more suited to outdoor use (I'm thinking if it's around hot pipes it might release fumes or something?)

 

@RayCaister - this looks interesting. Going by the product spec ('low post expansion') am I right in thinking this would be easier to work with that the normal yellow expanding foam that goes everywhere?

 

Low modulus just means it is still flexible when set so is ok for expanding and contracting pipes, you wont get any fumes from it once it has set

 

Correct. Although it is very impressive to watch the "yellow stuff" in action it can be a little too expansive.

 

@ianmcd @RayCaister

Thanks both for your replies. That has narrowed it down to two options, both of which sound like they will be good. I'll do a bit more reading up on these, cheers.