Mould and damp in attic space

My builder is coming next week, he has already said he's lifting slates or going via soffit. There is no room to work at the point the problem is at its worse, as it boarded for storage. The cross joists take you further from the soffit from the inside and makes a hard job impossible to do right. Victorian kid 100% 😂

Ill resurrect this one to see if the posters above are still active and might have any idea of the next conundrum.

So the builder was back, and after lifting slates found out that insulation had been packed into the actual soffit vent. So the pipes that were added had restricted airflow as the soffit itself was clogged. Should not have happened obviously, but resolved now at least by removing it all and ensuring the vents are clear.

So around/after this time we started to notice a smell coming from our MHRV unit (Its a vent Axia Sentinel Advanced). It is installed in the attic space, and vents via roof vents stale air, pulling clean air in about 3/4 m from extract vent.Alll ducting in the attic is insulated, and penetrates through the roof to supply/extract from the house below.

I would have to say its a musty smell, sometimes almost like a urine smell. Google would suggest it mold growing "somewhere" in the system. Sometimes we cannot smell at all, sometimes really strong…cannot find a pattern!

Ive had the installer back 3 times now and hes checked all vent, cleaned the mhrv with bleach and apart from a small bit of mold on the extract fan inside the unit o the extract to outside side, no major mold found. Given what happened in the attic its hard to not connect the 2 things, but this lad has opened up the manifold etc and says he cannot find any mold. So hes completely bamboozled, as are we!?

Thanks for reply: So I opened the unit and the gaskets and seal look fine. The unit closes very tight, so im fairly sure that its not taking air in from the attic space. The contractor opened the ducts from the outside supply vent to the unit and said they were clean/clear. No sign of mold etc. He then opened the manifold and said that was clear. He obviously didnt inspect all the ducts from the manifold to each room, so its possible that they are the cause. I'll look into this camera. It would need to be telescopic like as some of the ducts are from the attic to kitchen.

Attached 2 pics. One is the mold on the fan on the extract to outside…side. This had mold. We think this was back when we had the ventilation issue and the machine was in holiday mode and shut off. The supply fan on other side completely clean, and in general the inside was clean.

Good idea will do. The working theory on that is that I set it to holiday mode to go "off" rather than low. It was def humid in that space when I was away as it was pre vents being unclogged. It's in the extract side, so would make sense as it's the warm/humid air. Reading online it seems u never shut these off for a prolonged period as the house needs ventilation!! Silly mistake from me, won't happen again.

So it was a deep retrofit designed. They did airtightness etc. we would crack the occasional window with it but when I checked the holiday mode section it was set to off in holiday dates. The options are normal, low, off

Sad 🎺 moment. Should be low. Only recommends being off for cleaning etc