How do I get my landlord to pay the gas bill?

ugh, that sucks you have to deal with this. i'm not really sure what to advise but if you haven't already been, get over to tenant.net's forums and ask there. tenant.net also has lots of info about heating rights and such.

Forum:
http://www.tenant.net/phpBB2/

Tenant Info:
http://tenant.net/nyc.html

Unfortunately I don't have any great advice because your heat is still on, it's just the impending shut off that you're worried about.

I did find this on a NY State website:

HEATING SEASON

Heat must be supplied from October 1 through May 31, to tenants in multiple dwellings if: a) the outdoor temperature falls below 55 degrees Fahrenheit, between 6 A.M. and 10 P.M., each apartment must be heated to a temperature of at least 68 degrees Fahrenheit; (b) the outdoor temperature falls below 40 degrees Fahrenheit, between the hours of 10 P.M. and 6 A.M., each apartment must be heated to a temperature of at least 55 degrees Fahrenheit. (Multiple Dwelling Law § 79)

CONTINUATION OF UTILITY SERVICE

When the landlord of a multiple dwelling is delinquent in paying utility bills, the utility must give advance written notice to tenants and to certain government agencies of its intent to discontinue service. Service may not be discontinued if tenants pay the landlord's current bill directly to the utility company. Tenants can deduct these charges from future rent payments. The Public Service Commission can assist tenants with related problems.

If a landlord of a multiple dwelling fails to pay a utility bill and service is discontinued, tenants can receive payment for damages from the landlord. (Real Property Law § 235-a; Public Service Law §33)

From 2003-2005 I lived in a place where the heat was in and out all winter. I can tell you one thing you can do but it's definitely on the more aggressive end of things and you have to take a lot into account before you decide to go forward with it. (ie evaluate what kind of relationship you have with your landlord: is it outright war or is there room for dialogue?)

NYC has a Warranty of Habitability that applies to every lease signed. It means that the landlord must provide basic services and quality of living. Heat is one such thing.

While you can't withhold all your rent, you can take some money out of rent during a month when the heat is broken for an unreasonable amount of time (days or weeks, not hours). It's kind of ambiguous just how much money you're 'allowed' to take out of the rent. My friends negotiated with their landlord when their landlord redid their heating and regularly forced them to have to stay out of the apartment at certain times for a few months.

The whole idea behind this type of maneuver is to force your landlord to deal with the situation. The idea is not to actually get a lowered rent. Also it's going to make your landlord irate. But the point is that you're willing to pay full rent if he'll fix the heat. It's an aggressive way to force his/her hand.

As a side note, I'm not sure of this, but I don't know how likely Keyspan is to actually cut off heat to the building, especially if the landlord doesn't live on the premises. I know they send all kinds of threatening letters, but especially during winter/cold months, I don't think they're going to turn off your heat. Don't quote me on this, but it's something worth looking into.

On the topic of Warrant of Habitability, I found this on tenant.net:

WARRANTY OF HABITABILITY

The Warranty of Habitability is an important section of the New
York Real Property Law. It requires owners of buildings to keep
their premises safe, clean and in good repair. Both the common
areas of buildings and the interiors of apartments must be free
of any condition that is detrimental to a person's health, life
or safety.

Under the Warranty of Habitability, tenants frequently seek rent
abatements by withholding rental payments, in order to get a
service restored or a defective condition corrected. If there is
a need for an emergency repair that the owner refuses to address,
tenants may also contract privately to have the repair done, and
then deduct the cost from the rent.

An owner's liability is limited, however, if the cause of the
service disruption is the result of a labor dispute. If there is
such a strike, and the owner reaps a profit as a result, a court
may order the owner to "pass through" the saving to the tenant in
the form of a one-time rent reduction.

Before a tenant withholds rent, it is advisable to consult an
experienced tenant organizer, legislative office, or attorney in
order to assure that the law is being properly applied.

The legal procedures available under the Warranty of Habitability
are explained in greater detail in the section of this booklet
entitled, "Your Remedies."

Also this on the website I linked above:

If a landlord breaches the warranty, the tenant may sue for a rent reduction. The tenant may also withhold rent, but in response, the landlord may sue the tenant for non-payment of rent. In such a case, the tenant may countersue for breach of the warranty.

Rent reductions may be ordered if a court finds that the landlord violated the warranty of habitability. The reduction is computed by subtracting from the actual rent the estimated value of the apartment without the essential services.