Flame lift off from burner.

[owington]

Hi,
I have found a problem with a few bosch lpg water heaters at the site where i work. Basically they have been unused for a couple of months and upon firing up im getting flame lift off from the burner on 3 different heaters. I have removed and cleaned burner and injectors but still the same. After speaking to Worcester im told it must be a problem with the flue as gas pressure correct and no blockages. All the other water heaters on site work fine after cleaning and im completely stuck. I have checked all the flues for debris and nothing. The model is W275, does anyone have any experience of working on these. I have done a spillage test with a smoke pellet and they are all pulling fine. Any help would be greatly appreciated.
Thanks

 

[Atouchofgas]

Hi owington, not worked on these for a wee while but stating the obvious I take it the ventilation is ok, (100cm2), have you check the flue seals are not damaged

 

[owington]

Yeah mate, Ventilation fine and all flues look good. Even replaced a full flue on one to be sure. Two of us trying to figure it out today and could not find a reason. Baffling

 

[AWheating]

inner poc tube cut to short or coming away during installtion?

 

[diamondgas]

In all honesty owington I haven't a clue what appliance you're talking about, however with the lift off is the burner otherwise sharp blue or do you have a yellowing tip or visciating, floppy burner head? Are these OF, BF or FF? End of the day a flame is a flame and needs certain criteria to be stable. Try back to basics flame requirements, see what's not quite right imho ..

 

[Mike Jackson]

They're an OF water heater normally fitted in static caravans. The only reasons I can think of are excess flue pull, excess gas pressure or worn injectors.

We had a brand new Morco doing this a few weeks ago and couldn't find a fault with it so it had to be swapped under warranty.

 

[owington]

Hi Mike,
Thats right mate its a caravan site where the vast majority of water heaters are morco. Theses are all fine, it just seems strange that 3 different but identical heaters are giving the exact same problem. The flame is not yellow but stable blue diamond, and all the usual checks done during a CP2 are spot on.

 

[diamondgas]

Just checked out the mi's .... How old are the heaters? Looks like a basic multipoint design. I've known of lift off on OF NG appliances. Some occasions it occurs on initial light up then settles. Sometimes see the burner kind of yoyoing off the burner head! I'd be wanting to cast an eye over the heatexchanger, see if there are clean and clear. The Thorn apollo would give similar issues as the fins started to get clogged up & restricted, As did the Main Severn multipoints, the BF Main Severns also burned through their skirts which caused visciation too ... Hope this helps

 

[jtsplumbing]

Are they on Bottle gas ? you may have dirty bottles ! try swapping for new bottle, Check Press at govner,

 

[owington]

Thanks for the further replies lads. All 3 appliances are on bottled gas but as the fires and cookers are working fine I assume no issue with the bottles. The water heaters are about ten years old on average and have been run for 20/30 mins as we have previously had problems with lift off that corrected itself after a short period. didnt get a chance to go back and double check heat exchangers today as been too busy but will look into that.
Thanks

 

[diamondgas]

lift off that corrected itself after a short period.

Just sounds like a flue warming up owington IMO Some flues take a bit longer than others to get a pull that'll draw of the poc's, especially shorter or really long flues in my experience

 

[Hardy1]

checked gas pressures?

 

[owington]

Yes Hardy, gas pressure at 36 - 37mb. The flues are short with the appliances being in static caravans but this problem only seems to affect the bosch models which is what i find strange. Tech team arent much help as they say they have so few models in use they hardly get any calls. Checked the heat exchanger on a problem heater today and gave it a clean but still the same results. The vans only have showers so the heater is never going to run for long enough to affect the pull on the flue i wouldnt have thought. Ill report back when ive solved it. I wont be beat on this one.:6:

 

[Mike Jackson]

I ripped a Worcester out today and chucked a Morco in. Amongst other things the flame had started to lift but the water just wasn't getting hot.

 

[jtsplumbing]

I've started doing some of these sites as well , it seems that some flame lift of is ok as it will settle down, as long as you have a nice blue flame everything fine, another strange one with some Morco water heaters (Fan Flue) is burner starts B4 fan run's but thats what they do !!

 

[bennygas]

what an odd problem here eh? sounds like you're going about it the right way though. all i can think of is given the temporary nature, maybe thermal inversion/flue reversal, but to be frank, it sounds like you've almost proven this not to be the case. i know it's a pain right now, but what an interesting fault. good luck mate. when it lifts off, do the flames just sort of shrink away from the burner gradually, or does it just become sort of a cloud of plasma instantly? had this on some lpg rs nd wtr htrs in park homes and that was down to reduced primary air (giving sedate lift off), whereas in cases where I had this kind of messy instant plasma, it was down to flue blockage. I know you've exclude these to some extent already, and it's OF which is obviously quite different, but maybe the way in which lift off occurs could hint at the cause? i've never worked on these htrs before, so don't know quite what the set up is - think you've prob excluded this already but any flame retention ports tidy and pilot's all nice and clean/good size is it? would love to know solution, just another thought - is there any boxing in around/near the appliance - don't suppose that's reducing amount of dilution air accessing flue via draught diverter thereby affecting pull of flue upon combustion chamber? just a thought...(although most would quite rightly call it a long shot)