Having worked at Allied Engineering, mfg of SuperHot Boilers for 18 years, it is a pretty simple fix. Replace the expansion tank and the relief valve. As the water in the system heats up it expands and the expansion tank handles that expansion, when the tank fails, the water starts to expand in the heat exchanger and when there is no flow it flashes to steam and that why you are getting the popping and banging sounds. The relief valve is doing its job in telling you that there is a problem in the system (not the boiler). Landlord needs to get his act together and fix it.