I've got an old boiler, and when I shut it off last summer for 6 months, I had to bleed the air out of the gas line before I could light the pilot. This year the pilot is staying on. How do modern boilers cope which have electronic ignition?
Air in the gas line, if it appeared spontaneously, is a dangerous fault.
The pipework is purged when installing it in the first place. The boiler itself can also do a small purge sequence during ignition. If it fails to light then it will retry that a number of times before locking out. That's normally enough to clear any air, although sometime you may need to reset it and allow it to try again if there is lots of air to clear.
In normal circumstances there ought not be any air anyway unless the pipework has been worked on...
When I had my boiler off for 6 months, it took me 30 minutes of pressing= the ignition switch to purge it. The pilot doesn't let much through.
Or would an automatic boiler let more through using the main jets? Coul= d it perhaps tell the difference between gas and air?
Yeah.... pipes are 100.00000% leakproof and the gas coming into your hou= se is 100.00000% pure....
-- =
What=E2=80=99s black, white, and red all over and doesn=E2=80=99t fit th= rough a revolving door? A nun with a spear through her head.
I said "6 months".
Sigh. The gas inside the pipe is under pressure, so if you turn the gas off at the main and there's a small leak, it's true that the gas pressure in the pipe would reduce to 1 atmosphere over time. However, there's a world of difference between that and a significant quantity of air diffusing into the pipe.
I forgot I'd turned it off at the lever by the meter. I was thinking air was collecting in the boiler pipe while the cooker was used, but I changed it to an electric cooker!
Well I can tell you there was a LOT of air in the pipe after 6 months of being closed at both ends. Perhaps the boiler pilot or the main valve by the meter leaks very slowly, after all 6 months is a VERY long time. It certainly isn't leaking enough to smell any gas. And I doubt anyone has 100.00% leak proof pipes over 6 months, just like your car tyre won't stay up forever.
Unfortunately, you are effectively assuming that your car tyre would pump itself up. You're not daft enough to think that would happen to a car tyre but for some reason you think it could happen to your gas pipes.
Eh? I'm saying that the air leaks out of the tyre over time (i.e. the tyre is not 100% leakproof). In the same way, the pipe is not 100% leakproof, so air will get in and gas will get out. The pressure of mains gas is only very slightly over atmospheric, so once that extra bit of gas has leaked out, air can get in easily enough.
Can it?
Unless you have 100.00% leakproof pipes, of course. And mine did (or the boiler pilot or main shut off valve did).
No.
What makes you think this?
Don't you know what "spontaneously" means?
Yes, and it didn't happen in what we're discussing, as 6 months was available for it to appear.
It's not the same at all.
If you have a closed vessel with a pinprick opening then whenever there is a low or high and the pressure changes a little bit of the contents will come out, or air go in.
Once in diffusion will mix the gasses.
Andy
Good point, and one I hadn't thought of.
Just to put some figures on it, let's assume 3% of the gas in the vessel becomes replaced by air each week. (That's roughly consistent with a weather map I was looking at with pressure ranging from 1020 to 990.)
Then after 26 weeks, the proportion of gas in the pipe will be 0.97^26 =
45%.
How does the weather map know how big my leak is? It's small enough that I cannot smell gas.
Sounds about right, the pilot refused to light until I'd attempted it almost continuously for 20-30 minutes. The piping from the meter onwards is about 13.5 metres, 15mm pipe. Two thirds goes to the boiler, one third to what used to be a gas cooker, and is now a self-closed attachment on the end of the pipe. Maybe they don't self close properly?
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