Can I be unbalanced ?

[OFSO]

Came home after four weeks to a bitterly cold house with most, but not all, of the power on. Woodstove lit but couldn't get the balanced flue central heating to fire up. After much thinking I took the front off the heating boiler, whereupon it started first time. This suggests, of course. a flue problem.
Question for all you heating experts out there. My heating boiler is designed for balanced flue OR unbalanced flue, and has knockout panels in the top to enable the latter installation drawing ambient air in from the room it's installed in. As the system is obviously having trouble drawing air in thru the concentric flue tube to the outside air (it's a very long run) can anyone see a problem taking one of the knockout panels out to provide extra ambient air ?

[Opsboi]

Mmmm

I'd go back to Teddington personally

[OFSO]

Yes but the boiler there, of course, has an internal leak ! Used to be a monthly top-up, then weekly, then daily, then twice daily. We were on tenterhooks that it might fail before we left but it held out
Incidentally had a quote for an electric combi boiler. £10,000. No thanks. New gas one, state of the art, £3,000.

[izod tester]

Provided the room with the boiler in is sufficiently well ventilated to provide sufficient oxygen to the boiler there should be no problem. If there is insufficient oxygen supply then combustion will be incomplete and CO will be exhausted instead of CO2. Some of the CO could find it's way into the room and poison the occupants.

[OFSO]

Thanks. There's sufficient combustion air. Boiler room vented into huge pool room, itself vented to exterior.

The older heating boiler in the same room wasn't balanced flu and did very well on ambient air.

[johngreen]

The manufacturers of such equipment most usually have very clear instructions about what they do - or not - approve of by way of installation requirements with regard to flue length, how many bends etc. If the present flue is too long or wrongly designed for the installation this should be corrected or the reason determined why the control system now finds fault with the breathing - assuming it has worked correctly before now.
There will be a pressure switch that senses the correct flow of air through the tubes, commonly a diaphragm type device attached to a venturi but maybe a piezo sensor nowadays, but the pressure being measured is not very great. The sensor could be temporarily upset by a period of misuse, either inlet or outlet of the flue could have become partially blocked by animals building homes in the nice quiet and safe environment or perhaps local atmospheric conditions at the flue terminal are having a negative effect of its performance.
Complete installation instructions can usually be found online without too much trouble.

There are many examples worldwide of very unpleasant results when such equipment has been wrongly installed and while I understand from your previous comments that finding competent workpeople is not so easy, I would suggest that at the very least, you refer to the manufacturers instructions before trying to modify the present installation.
It would be a great shame to learn that you (or any one else for that matter!) had gone to meet your/their maker on the crest of an explosive wave or succumbed to the effects of CO.
If nothing else, the Ops-Normal crew would surely miss you and your commentaries terribly...

[talmacapt]

Is the balanced flue a newly installed system or has it worked for some time and now stopped drawing sufficient air?

If it has started happening and nothing else has changed, I would start by ensuring that nothing is blocking the air-in tube (bird's nest, insect nest etc.).

I can't, from what you describe, see a problem, in the short term, by running with taking out a panel but it may be better to solve the actual problem.

Due you have a CO alarm?

If not, fit one!!

I wrote this before john posted but willleave it.

[OFSO]

Yes, alarm fitted and at right height.
The manufacturers installation instructions show the boiler as either
(a) a balanced flue installation
(b) drawing air for combustion thru ducting to an outside wall
(c) drawing ambient air for combustion from the room in which the system is located.
In both cases (b) and (c) the air is drawn in thru the blanking plate I have removed.
The previous installation was a non-balanced flue and hence the room in which it's located has permanent uninterrupted ventilation to the outside air.

[OFSO]

The flue in/out ducting must be about 20' long, runs thru the lower floor tower foundation, very difficult to get to and hence hard to inspect. From the outside it looks clear of insect and mammal incursions but who knows.

[talmacapt]

You have a problem, I would live with your solution for this winter and try to fix it when it gets warmer.

What you need is a very long boroscope.

It was -5 at 1600 yesterday and -20 at 2230 eventually getting to -22 from 0200 until 0500.

Midday now and we are back to -7.

My problem is the underfloor heating can't keep up with these kind of changes over such short periods of time and as a consequence it was a bit cold last night and like a sauna this morning.

Outside grilli for a BBQ this afternoon, I think.

[OFSO]

Reading the UK boiler regs., the maximum balanced flue length should be not more than ten metres. Every right angled bend adds a theoretical metre. No mention of the decreased efficiency of horizontal v. vertical flues. Comment added that ignition difficulties may be experienced over this limit (that's what I had).
My installation is borderline for length. There is a picture in the installation manual showing one of the ambient air intake blanking plugs being removed with a cryptic comment in Castilliano that this may be necessary if the flue is folded.
After a week, no fumes in boiler room, no warning from carbon monoxide sensor, boiler running happily.