Boiler advice

This is probably not totally DIY, but has anyone got any comments on condensing boilers. My present (old fashioned) one is over 20 years old - now that was a DIY install - but is suffering from an intermittent fault and SWMBO wants her warmth. Comments on reliability would be welcome, as on the complexity of installing. How much of the kitchen & plumbing needs to be rebuilt? (for instance)
Fault is that it's tripping out. This morning I could hear localised boiling within the boiler and then it cut out. Any idea what's causing that boiling? Do I simply need to add some more corrosion inhibitor?
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Did the same a few years ago. The old floorstander was replaced by a wall mounted one - but since it was in a cupboard, disruption to other things was a minimum. Generally most new condensers are smaller than older boilers. Only addition was a cold water feed to it. As it is pressurised rather than open vent with header tank as before. The flue of course is different and smaller from the old BF terminal, so that needed bricking up and a new hole made.

It can probably be fixed. Make and model will be needed. However, with the constant escalation of fuel prices a more efficient boiler makes even more sense.
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On Fri, 14 Oct 2011 10:00:24 +0100, "Dave Plowman (News)"

And somewhere to drain the condensate is needed. Also condensing boilers work best at lower temperatures so you may need to uprate your radiators.
You can get heating only condensing boilers so you might not have to convert a vented system to sealed if you don't want. However I much prefer the latter.

I'm usually of the opinion that repair is better than replacement. A modern condensing boiler will be cheaper to run but they are far more complex and, IMHO, not likely to last as long. Without a crystal ball to predict fuel prices I can't say which option would be cheapest in the long run.
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It, of course, depends on how big your gas bill is. However, I can't really see gas prices doing anything but increasing in the foreseeable future.
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I don't believe there's been any fair comparison between a long-life iron lump and the modern, relatively short lived, less reliable and costly to maintain equivalent. No doubt they are better for the planet but I'm not sure the pocket benefits like they say !
Andy C
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Cast iron isn't the issue. SS heat exchangers have a long life too. Just how long the extra electronics which are part of a modern boiler last is down to design. Boilers built down to a cut throat price are likely to be just as reliable as any other similarly engineered product. ;-(
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On 14/10/2011 14:15, Dave Plowman (News) wrote:

Indeed. Also the larger your bills then the quicker the potential pay back.
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wrote:

Indeed, I guess the next best thing one could do would be to get a simple heat only boiler with a SS heat exchanger (Vaillant, Viessmann etc) and then have all external controls, external pump, external valves, external EV etc.
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charles wrote:

If you replace with a non-combi non-system condensing boiler (i.e. fed at low pressure from a header tank in the loft) then the plumbing is almost the same - gas in, water from and to rads and HW tank. Additionally you'll have a condensate drain, which needs to go from the boiler into a waste outlet or outside to a drain. The new boiler will be room sealed so ideally should go on an outside wall.

Is your pump working?
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yes, the pump is working - when the boiler trips out, I can hear the water being pumped round.
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The fault you describe and localised boiling could be down to a pump on its way out or the boiler may need descaling. Since a new boiler would require a chemical clean to the system anyway why not carry out a chemical clean anyway the see if your problem has gone away? Have a look into the pump as well before throwing mega bucks at what might be a tens of pounds repair.
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Indeed, it sounds like it has to be either pump or a blockage, either of which is far cheaper to resolve than a new boiler.
NT
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In article

I'm sure the pump is fine - so, descaling could well be the answer. I do hear tehn odd air bubble in the boiler area from time to time. Perhaps the system is bringing in air through a slightly weepy rad valve? After a descale, I should use a leak seal agent?
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It really does sound like a flow problem - pump become ineffective or blockage.
What temperature is the boiler set to, and does it get better if you turn it down?

Is it a vented or sealed system? Is the water changed or topped up often (has it leaked at some point)? Inhibitor?
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That doesn't make any difference - tried that in the past. It has been playing up for over a year, but hardly at all during the summer when it only heats the hot water (valve isolated). So perhaps sludge is circulating from the rads in the colder weather.

vented
I replaced that last time I had to changed a valve. I've always used Fernox before, but the place I went to only had Sentinel. I cabn'y believe that's teh problem, but perhaps it's not as concentrated and therefore not doing its job.
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In that case, it sounds like the heating circuit is blocked, and the hot water circuit is OK.
Has someone closed down radiator valves, and what forms the bypass circuit? Has your isolating valve really opened?
Does the system have a mid-position valve to select HW/both/Heating? If so, does it work OK when there's demand for both HW and heating?
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The radiators all get hot.

the bypass circuit is two fold. One close to the boiler (as per manufacturer's installation instructions) and another is simply an uncontrolled radiator. Possibly - 23 years after fitting - the one near the boiler isn't working as it should. Perhaps I should fully open the valve and then reclose to the correct point.

Two separate valves. But this not a permanent fault; it can go for days (weeks sometimes) working quite normally and then suddenly the boiler trips. Today was teh first time I've been ithe room when it happened and heared the bubbling/kettling noise. I've put a jar of Sentinel System Cleaner in, and I'll drain it in the middle of next week. Then I'll see what happens.
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What make boiler? Is there a pump over-run circuit? Even in a 'perfect' system, if the pump stops while the boiler is firing it may boil before shutting down. So you'd normally arrange for the pump to carry on running for a short while after the boiler is told to stop.
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Glowworm
Of course. It's in the buit-in controller.

Of course. Remember this is a fault that appeared after 21 years of sucessfull operation, so I doubt very much that's it's a system design fault.
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Blood out of a stone ...
what model?

Which controller ?
21 years old? Not necessarily
does the pump overrun actually work?

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geoff

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