Gas Geysers problematic in winter

We bought three (2 x16L and 1 x 12L) Zero Appliances gas geysers in the last four months when we decided to convert to gas geysers in our rooms to avoid loadshedding. We have had endless issues with them since the start of winter. They cut right in the middle of a shower and bring in cold water without warning.

Our guests suffered the trauma of having to endure cold water in the middle of a warm shower. Due to the nature of our business - Guesthouse, we couldn't even send them for repairs. To be honest I don't even think i want them repaired. We have since brought in another brand and we have had no problems since.