Does a combi boiler need a bigger gas pipe than boiler with large water tank?

A 'combi boiler' would draw off more gas in a shorter period of time as the hot water is instantaneously heated, as opposed to a 'heat only' or 'system boiler' where they would heat a HW cylinder over a period up to an hour. Little behold to upsize a 15mm gas pipe to 22mm or even 28mm is not a difficult job. Hope this helps. DC Plumbing & Heating

You have not mentioned the make & model of the proposed boiler, so we cannot answer your question. But the majority of new condensing combi boilers do require a 22mm gas feed. Just because the other installers did not mention this then they may have over looked this important factor. The installer(s) should as good practise when quoting to renew your boiler carry out a gas pipe sizing exercise, to ensure no one gas appliance is starved of gas when all appliances are running simultaneously. Ask the installer who stated the increase of gas pipe if he did indeed carry out this exercise, if necessary? Based on the updated information of your proposed boiler it does require a 22mm gas feed. You can easily check this out by simply ringing Worcester Bosch technical support.

The Worcester 32 compact would need a 22mm supply pipe and possibly upgrade the pipe from the meter to 28mm depending on what appliances you have in your property. The allowed drop for a Worcester 32 is 2.5mb from the meter to the inlet pressure at the boiler with appliances working.

The Worcester 32 compact would need 22mm pipe running to it and may even need to upgrade the gas supply to 28mm dependant on distance and other appliances which are also on the supply.