The big fire under my boiler wont light?

Just recently our water heater/boiler stopped working. We had no hot water, so we called the customer help number on the front of the boiler. They diagnosed it with all sorts of problems and sent me like 4 different parts. we installed them and the boiler light turned back on, but not the big light that it used to have before, under the smaller one. so we only have enough hot water for one of us to shower a day. if anybody knows how to fix it or can help me with my problem please write back OK thank you!!!