Had a condensate pipe joint leak going into an external wall, the plaster was destroyed over 6 months until i noticed and sealed the leak. I also have 2 combis running into a victorian drain and over 2 years the clay pipe cement joints have now been destroyed, allowing the drains to leak into the surrounding soil. I know this as prior to installing the boilers, i tested the drains to ensure they didnt leak as I wanted to check they were secure and sound before conveting the property into flats. The manhole the condensate runs through has now become a rough surface, where before it was smoooth as it should be.
So guys, despite what you may bellieve, if the flats are used intermittently by owners, and the heating is left on, cement joints etc will be damaged, I have the proof at this property so any means of reducing the damage needs to be looked at as some properties will suffer damage in the long term.