Bottled gas lines

[Kittyhawk]

This relates to the gas installation in my motorhome.
Basically, the gas line from the bottle and regulator to the hob/oven is about 6m long. The hob/stove is at the end of the run. About halfway along the gas line there is a tee and a branch gas pipe goes to the water boiler. This pipe would be about 2.5m long. The water boiler is new and it and it's predisessor will keep flaming out 4 - 5 times after starting, and then it will settle down and function normally. We use the water boiler as an 'on demand' appliance, only firing it up when we need hot water.
The only reason for the boiler flame outs that I can think of is that the gas flow to the hob/stove is partially evacuating the boiler line and causing air locks in it. I'm out of my depth with this gas stuff and don't know if this is even feasible. Advice appreciated.

 

[ChaiLatte]

You do not say if this is a professional build nor whether both appliances were in the vehicle from new.

What gas is it? What regulator is it?

If you read the specifications of the two devices, you will find gas demand numbers. You can then look at the diameter and length of the pipe in conjunction with the gas pressure and see if it is adequate for the demand.

With (low pressure) natural gas in the UK, the rule of thumb (good for 90% of standard cases without more detailed analysis) is 22mm diameter pipe to within 1m of the boiler to ensure the allowable pressure reduction is not exceeded.

LPG will have similar detailed rules and rules of thumb that work in most cases.

Put a non-return valve as close to the boiler branch of the tee as possible. Then if your theory about the stove is justified, it will cure it.

If each appliance works OK on its own, install separate pipes and supply each one off its own regulator and bottle. Complete independence.

 

[Tris]

Sounds like bad gas pressure if both the old and new one do it. It is possible to check your system pressure with a manometer yourself. That will tell you if the regulator is providing the right pressure, and then whether you have any leaks.
Once that's checked and ok it's on to testing the flame failure device and if that passes look at the pipework for anything that may constrict the flow, including bad joints on the tee junction

I'm not a gas engineer but this is from years of caravans and motorhomes and how we'd go through it with the workshop

 

[Kittyhawk]

It is a factory supplied professional installation, both appliances in the vehicle since new. The replacement water boiler is a Truma as was the original. Gas is LPG. Gas regulator is quite ancient and possibly should be renewed. Once the initial flame outs with the boiler are over, both appliances work faultless singly or in unison. Have soapy water checked all lines and connections for leaks.
The fact that I have to do 4 - 5 restarts of the boiler on start up is not a big problem. It's just a minor aggravation but annoying because I don't know why it does that. At start up it will usually run for a minute or two between flame outs, then settle down and run perfectly. There are no issues with the hob/oven.

 

[Tris]

To be honest there's some UK based manufacturers whose quality control on installations leaves a lot to be desired, but Truma stuff is normally good. Anything in the handbook about flame failure?

 

[Kittyhawk]

An update.
Current suspect for the flame out issue is the LPG regulator. Firstly it appears to be original equipment which would make it 12 years old - do these things have a life expectancy? Secondly I can see that the plastic cap over the regulator adjusting screw has been priced off a few times which would imply that the delivery pressure has been tinkered with.
The stove handbook does not state LPG pressure so assume that it's not too fussy. The Truma boiler asks for LPG at 30 mbar. Without knowing what else to do I fired up one burner on the stove and then turned on the boiler whereupon it worked without and flameouts. Once it was properly warmed up and running I shut down the stove burner and all ok with the boiler. Presume the pressure from the regulator is initially too high for the Truma?
Thank-you for the replies - I appreciate them and just wish I knew more about gas reticulation.

 

[Spectric]

I'm out of my depth with this gas stuff and don't know if this is even feasible. Advice appreciated.

Do not get involved, take the vehicle to a specialist as there is more to Propane / Butane gas instalation than meets the eye. With poor install you can have issues with liquid in the lines or other issues that could effect safety.

 

[Tris]

UK recommendations are to replace the Flexi hose every 5 years, and the regulator every 10, so definitely worth it

Over here a decent regulator will set you back about £25, add an hour's labour somewhere you trust to do the job and you should be sorted