Undersized gas pipes- Already well covered on here I know

[TerryWaite]

would like to know what you would classify a boiler reading 17-18mb inlet working pressure with the cooker running. And is undergassing as dangerous as overgassing, obviously if an appliance is overgassed incomplete combustion could occur and thus CO, but if an appliance is undergassed surely it should definitely be getting the full amount of combustion air, is the issue more that of the flame going out, or does it create other problems?

And also what causes the loud bang when a boiler is undergassed?

 

[SimonJohns]

Te loud bang comes from the lack of has in the ignition mix causing a build up if gas. Then the whole chamber explodes rather than the burner lighting

Under gassing Can cause many different out puts. But usually it can be fine. All you would norm get is poor performance

 

[gasmarc]

I though dodgy electrodes or burner ,spark, over gassed seals etc can cause explosive ignition

 

[diamondgas]

I've had experience of a modern zero governed boiler dropping the inlet to 9mbar yet still 'sucking' it's correct volume of gas in! main issue is on other appliances, such as cookers that religh on 20mb, therabouts, for safe working! IMO

Undergassing is different! Usually flame lift on pre-mix burners such as the modern boilers now have...

 

[tamz]

How you would class (if at all) it is very much dependant on the boiler and what the mi's say and did you also check the working pressure at the meter to see what the pressure drop was.
At worst class as NCS.

 

[Kev the gas]

I have found gas fires spilling POC badly, due to low inlet pressures in the past.

 

[johnnyplumb]

i would check working pressure at meter, if 19mb then 18mb at boiler ok . i was taught overgassing worse than undergassing

 

[marleyco]

I have found gas fires spilling POC badly, due to low inlet pressures in the past.

You might have just made me realise why the fire I checked for landlord was slightly spilling. I had 3 to 4 mbar under. Signs of spillage evident when I removed fire. Just the foam seal stopping soot spreading further up the fire surround. I failed it.

 

[DJNelsonHeating]

Generally slight underpressure for boilers is OK, provided the burner pressure on max is achieved, though the MIs are always the first port of call for advice.

 

[Shaunthegas]

Over and Under gassed are both ID situations. (over and you'll get a huge CO reading)
However read MIs and also contact technical to double check to relate your readings.

For example VAillant specify 16mb is the lowest OP of a ecotec pro24 combi. They also give a maximum of 23mb, but in between is ideal.

Also check your gas rate, if its +/- 5% the nominal reading, then your fine. If your OP is good but your gas rate not. Then you've got to increase the pipe size.

 

[GrahamM]

This is not an automatic ID as mentioned in previous post. What safety classification you give is dependent on a number of factors. The specific appliance, how the appliance is affected, other appliances, your safety readings & visuals, all come into play here. Only then can a judgment on the classification of safety be given.