If you are planning to switch your old gravity based hot water system with something more efficient and advanced then there are many factors to consider. If you got a sales pitch to install a pressurized system because of its potential output then first know what will be the total cost of purchase and installation.
Evaluate main pressure system
Consult with water supplier to find the flow rates and water pressure supply to your property before deciding on gravity boiler replacement. If the flow rate or pressure is lower than the necessary level of new mains then consider another alternative because fitting water pump to main supply is illegal.
If the flow rate and pressure is suitable then check if it is sufficient inside the property. Pipework diameter from main supply towards your property can be narrow, so adequate flow cannot be maintained. You will need to consider the cost of installing new water supply pipe.
Evaluate gas supply pipe
Diameter of the gas supply pipe needs to have enough gas flow, so that the new boiler can work efficiently. The old supply pipes can be narrow and can need replacement, so consider this potential cost.
Check central heating system
The old pipe work may not be able to handle the pressure of gravity fed to the mains and can collapse, so replacing total central heating network is necessary. A potential added cost!
Hot water storage cylinder
High pressure cylinders are made from steel, which includes a special pressure releasing safety device. The existing low-pressure copper cylinder will be unable to withstand high pressure, so need to be replaced.
Make sure get approval before installing the un-vented main pressure system. Annual inspection is legally obligatory and it also ensures that the unit is operating safely. Proper installation means your hot water supply needs are met and you get an energy efficient boiler system.
Before you just go and buy the gravity-based boiler system consider the overall cost including purchase, installation, maintenance and safety!