If you live there permanently does it need to be on continuously ? I don’t have any VMC in this place and there’s no dampness whether I’m there or absent for a few weeks.Each property is different I supppose.

You may find hat switching from 1 to 2 just changes the speed of the inbuilt fan. They should be installed so that they cannot be turned off - except by cutting power at the electricity circuit board (tableau).

AS for maintenance, ours is installed in a place that is completely inaccessible so has received no maintenance in 15 years.

there seems to be a lot of conflicting advice here about the VCM. The units available from the brico are mostly only extraction fans, they have 3, 4 or more 80mm dia connections for toilets and bathrooms and one 125mm connection for the kitchen. they usually have two speeds. These units hang in the loft on a nylon string suspension to avoid any noise transmission made through the more firmer fixed bracket type of fixture. having them on permanently seems pointless and can best be started by a proximity sensor in the space to be vented (toilet, bathroom etc.). Replacement fresh air is allowed into the spaces by vent grills or fanlight windows etc. In really modern houses, a VCM also includes a heat exchanger and ducting to bring in fresh air to replace the air exhausted. The heat exchanger removes the heat from the outgoing air and transfers it to the incoming fresh air. These are complicated systems with ducts to and from the rooms that are being vented. These systems may even have a humidity sensor or some other control system to operate automatically.
Old stone houses have always been built to allow the walls to breath and if the house gets refurbished with modern insulation and placo everywhere, then one should take into account the requirement to have air spaces between the insulation and the wall that allows air to circulate, forced ventilation is not normally required for this.
There you go. That's my pennothworth, pick the bones out of that.

I was told almost 20 years ago by an Estate Agent that VMC's were intoduced as most French houses have larger windows on the front of the house and historically south facing to gain maximum light and heat through the glass, on the rear of the property would be smaller windows if any and that is where the stale air gathers and causes infections, VMC's were introduced to move the air in the property to take out stale, maybe infected air.

In Brittany where it was mainly farming back in the day, peasants would literally put themselves to bed after all the crops were in around Autumn and come out of their houses in early spring, it is believed their metabolism would naturally slow down and they could survive the winter on minimal food, very similar to the mediterranean diet but the problem was that whole families would share a bed and any illness would spread quickly. We had a house with a barn but it was actually the peasant quarters on the farm, it had a chimney plus either side of the chimney were window like holes in the wall were the animals were next door and the heat from the animals would contribute to heating the house, from that you can see that animal illness and human illness went back and forth.

The problem with VMCs is that they suck warm air out of the house and replace it with cold, thus increasing your heating bills. My policy is to run the VMC part time and definitely not when the weather is very cold.

Understandable but that is exactlly the time it is most needed.