My gas water heater which is located upstairs, is leaking. There is water in the pan and some water is showing on my downstairs ceiling. Is the water heater broken and/or is a pipe in the wall leaking?

Boilers are inherently dangerous for the average DIY for so many reasons, contact British Gas and have them come back and fix it, tell them it was fine before the "service". They may simply have a control valve shut off.

Let's walk our way thru this one: I assume you have an upstairs shower, and a downstairs shower?-- Are you able to follow the pipes coming out of the Hot Water Heater?-- Can you trace where the pipes to the upstairs shower go?-- And what about the pipes to the lower shower? -- Do they BOTH come off the HOT water pipes coming out of the top of the HW Heater?
A big help in tracing pipes, is by having the hot water run in the Shower that is getting HOT water-- Feel the HOT! pipe?-- Now-- shut that water off, and go to the lower shower-- When it is running, can you hear water flowing out of the pipes at the top of the Hot Water Tanks?-- or do you feel Cold water moving-- Can you travels where it is flowing from? Get back with me, and tell me what you are feeling, and hearing-- Mack B

Probably bad news if steel tank is leaking.

1) Copy following link for do-it-yourself troubleshoot walk-thru:
http://waterheatertimer.org/Leaking-water-heater.html

2) Drain tank and set in a drip pan with drain line to outdoors.
http://waterheatertimer.org/images/Water-heater-drip-pan-2.jpg
http://waterheatertimer.org/Water-heater-will-not-drain.html

3) If tank ruptures, it will flood home

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Absolute danger here:

1) Call gas company IMMEDIATELY to check for gas leak that can cause explosion and fire.

2) Call plumber immediately to fix improper combustion or improper vent before toxic combustion by-product kills family.
Gas appliances must vent toxic by-product outside and away from home where the gasses will kill the planet instead of you.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Copy following link for troubleshooting leaking water heater.
http://waterheatertimer.org/Leaking-water-heater.html

You posted question under propane gas heater.
Propane is heavier and air, and this type gas water heater should not be installed in basement (below grade) since gas leak can fill basement with explosive gas.
Water leak does not cause gas leak, so water leak is separate problem.
Recommended for propane safety: install gas detector close to floor near gas water heater
Regular Natural Gas heater, install gas detector higher on wall since NG is lighter than air and will rise.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Plumber is right.
Problem is not amount of air in attic. Problem is how hot the air is.
Oxygen molecules separate apart in very hot air and pilot light goes out since there is not enough oxygen density to support combustion.
http://waterheatertimer.org/images/Water-heater-in-attic-800.jpg
http://waterheatertimer.org/pdf/Attic-Ventilation-and-Pilot-Outage-in-Gas%20Water-Heaters.pdf

More ventilation is needed.
Plumber is not ventilating expert, and not responsible for attic ventilation that builder failed to install. Plumber should do a survey of location before installation to make sure gasoline vapors are not stored nearby, but summer attic ventilation is gray area until more general-public folks become aware of problem. Hotter summers temperatures will spread that information.

Hire local home center to install roof vents AND soffit vents.
Note: You also need soffit vents.
Remember a vent on the roof is like sucking air out of a coke bottle. The roof vent is no good unless air can also enter the attic from another vent located in the soffit.

Another solution is electric water heater for very hot locations.
Or install solar-assisted water heater.
http://www.hotwater.com/products/residential/cirrex_solar.html

Make sure the air is bled from the upstairs rads.
[air = top of rad is cold & bottom hot]

If you need to balance the rads to maintain an even flow through all then :-
Turn off all rads [one valve fully open and the other closed] Get heat going and open each rad valve, in turn, about 1 or 2 turns. Start with upstairs. The position you need to get to is when the return pipe fron each rad is a few degrees below the flow pipe. Adjust each rad valve to get this effect a few times may be necessary

Is there any water at all coming out? If not turn the cold water tap on the hot water tank on.

Hi Leehardcast,

Yes the problems are related. The system is low on water. So now instead of water you have air in radiators which is easily compressed when it heats up. Then pressure loss when it cools down.

Add some water to your system until you have 15lb pressure and bleed out upstairs radiators at the same time.

Please rate this response and Good luck, Phil