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The gas piping from my gas meter comes into my house in a straight 10 foot run to my gas furnace

Two feet from the exterior wall the black pipe has a t connection with a run to a gas dryer. The gas dryer works fine but the 3 year old gas furnace has a supply problem.

The furnace initially ignites okay with a gas pressure reading of 7 but when the burners go to the second stage the gas pressure drops to a .5.

I have been advised that there is a possibility that there is an obstruction in the black pipe. Here are my questions

is it possible that the gas valve adjusting the flame might be bad?

How would the possible obstruction in the black pipe be cleared?

What type of professional should I hire to address this? An HVAC tech or a plumber?

Is black pipe still the only acceptable material used for gas distribution in the home?

Thanks for your help

  • if it's after the meter, i think you'll need a plumber... – dandavis Oct 7 '17 at 10:38
  • Or a steamfitter. – Lee Sam Oct 7 '17 at 16:26
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    Licensed HVAC technician, as you are not certain the problem lies within the pipes. Once the technician diagnoses and confirms proper operation of HVAC equipment (or fixes it), he will tell you if he is qualified to perform repairs on upstream gas supply piping if necessary. If not, then licensed plumber. – Jimmy Fix-it Oct 7 '17 at 22:19
  • HVAC repair tech, with a van that says they also do boilers; pretty good chance they have pipe fitting experience. Any legit 'hvac' company that only does new installs prob won't do electrical or any plumbing beyond a condensate line. - Hire the one who says the problem (was, now it's worse) is that there's no drop leg. – Mazura Sep 19 at 2:42
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To address the gas pipe blockage or a possible leakage the professional you should contact is your gas company. They should have service personnel just for this sort of work.

is it possible that the gas valve adjusting the flame might be bad?

Yes

How would the possible obstruction in the black pipe be cleared?

Replace the pipe.

What type of professional should I hire to address this? An HVAC tech or a plumber?

Neither one. Contact your gas company for a certified gas repair technician.

Is black pipe still the only acceptable material used for gas distribution in the home?

This might vary by location - In USA - state, city, county, federal codes govern this. Search for Gas certified pip and you will see a range of pipe available (not necessarily in compliance with building codes - but what is available to be used).

  • Ken, thanks for your reply but in MD the gas utility will only repair their meter and outside. The inside has to be contracted by the owner – provlima Oct 7 '17 at 19:22
  • @provlima find an appliance repair company that services gas appliances - they should have a certified gas repair tech. Any blocked Gas pipe should be replaced . There is a reason it is blocked. If the pipe is blocked it is also possible the feed controls on your downstream appliances have a blockage as well , make sure they are thorough . Identify how it became blocked..from upstream or what ... ask and inform in your questions the concern for the origination of the problem not just the replacement of a blocked pipe. (Some repair people need a hint that it did not just block all by itself). – Ken Oct 8 '17 at 19:41
  • Ken,thanks for your reply. What I can't understand is why does the furnace receive a 7+ inches of pressure during the 90 seconds of the first stage ignition, but then suddenly drop to .3 when the second stage kicks in? – provlima Oct 8 '17 at 22:43
  • @provlima depending on how you are measuring the pressure - it is natural that your pressure drops when the second stage kicks in the volume of gas it requires to run. Think of a balloon or a tire - while the air is inside it maintains a pressure once you call for flow of air (releasing from the balloon or tire) the pressure drops.Since your supply line is not like a tire or balloon with a fixed amount of gas - in order to maintain the pressure - your flow rate must at least match the consumption rate. – Ken Oct 9 '17 at 1:24

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