Probably a stupid question, but this summer I had to drain and then refill my hot water heating system. Since it was warm, all the TRVs were off. But what happened to the water in the supply pipes? With the TRVs closed, I couldn't bleed or refill those sections.
I suppose they can drain out by bubbling/gurgling out, but after refilling, do I have air in there?
To be very explicit, consider an upward section of supply pipe ending in a TRV. How do I refill those pipes when the weather is so warm that the TRV is closed even at its highest setting?