The first radiator gave a long, thin hiss, like a bicycle tyre losing an argument, and Matt, kneeling beside me with a jam jar, said, "That's Dennis's air." It was about quarter to seven on Sunday 23 March. I gave the key another eighth of a turn, the hiss turned into a spit, a bead of water appeared at the valve and I shut it.
We have seven radiators: front room, back room, kitchen, bathroom, and one in each of the three bedrooms. The heating had been slow all March, and the box room, where I work two days a week, was warm in the middle and cold round the edges. The engineer at the boiler service on 6 March had said the radiators were probably holding air and told me how he'd go about it. The radiator key came from Screwfix and cost £3. The jam jar had held lemon curd, so that was free.
The order, the towels and the hiss
We turned the heating off an hour beforehand so the radiators were cool. Then we went round in the order the engineer gave me: downstairs first, then upstairs, and on each floor the radiator furthest from the boiler first. That meant front room, back room, kitchen, then front bedroom, box room, back bedroom and the bathroom. Matt held the jar and a towel under each valve while I turned the key a quarter turn anticlockwise and listened.
The downstairs ones were quick: five seconds of air in the front room, a splutter in the back room, water straight away in the kitchen. Upstairs was a different story. The front bedroom hissed for about fifteen seconds. The box room hissed for nearly a minute, which explained a great deal about my ankles on a Wednesday afternoon. The bathroom gave up a couple of puffs. The whole job took about forty minutes and the jar caught perhaps two tablespoons of water.
My mistake came in the front bedroom, where I forgot the towel for roughly three seconds. A thin line of brownish water ran down the wall and onto the carpet and dried into a faint stain. Matt says it adds character. I would have liked to take the character on a different occasion.
The pressure bit
Letting air out of a sealed system pulls the pressure down. The gauge on the boiler, which lives in the kitchen cupboard, had read about 1.3 bar when I started, and afterwards the needle was sitting at 0.5. I had a PDF of the manual open on my phone and the engineer's quick lesson from the service in my head. The filling loop is a short braided hose under the boiler with a valve at each end. You open one slowly, watch the needle and close it again at 1.2 bar, which took me about ninety seconds and one held breath. Ours says between 1 and 1.5 bar when the system is cold, so that was the range I aimed for.
That is as far as I'll go with the boiler. Anything with a gas pipe stays with the engineer, and the manual and the filling loop are the only parts I'm happy to touch.
The one that stayed cold
With the heating back on, I put a hand flat on each radiator in turn. Six were hot across the whole panel, and the box room was warm from corner to corner by 7.15am on Monday, which it had never managed since we moved in. The back bedroom radiator was hot along the top and stone cold across the bottom third. Matt laid his palm on it, looked at me and said, "That's not air."
Cold at the bottom and hot at the top usually points to sludge settling in the radiator, and it was just what the engineer had mentioned on 6 March. He had recommended a magnetic filter on the boiler pipework, a small device that catches rusty debris before it gets into the radiators. We haven't had it fitted. A £720 consumer unit had gone in nine days earlier and the filter lost the argument. It sits on the list under "later". It is also the room with the mouldy corner, so the back bedroom is currently winning the contest for most things wrong with a single room.
Total spend on the evening: a £3 key and a jam jar. The house tab got the £3.
