Defer to the manufacturer’s instructions for seismic strap installation. According the baxi’s own list of error codes, the 118 fault is directly related to low water pressure in the boiler. Why does a system upgrade take longer than other installations? to explain, take switching a system boiler for a combi boiler as one (the system boiler) features a cylinder, and the other doesn’t, the engineer needs to first take away the cylinder and then re-pipe your central heating system. It's not just timeliness.