Combi Boiler with accumulator

At present we have a Saunier Duval combi boiler together with a 150Lt accumulator, both of which are situated in the basement and water is circulated by a Grundfos pump. Our gas bills are astronomical and we suspect that a good part can be attributed to the boiler constantly firing up to keep the water in the accumulator at the set temperature. The pump too is operational for a good part of the day. Looking for ways to economise, a neighbour has said that we should effectively turn off the accumulator and only heat the water as and when required through the boiler. We realise that whereas we have instant hot water now, we would, if we bypassed the accumulator, have to wait for the water to heat and come through but this would be acceptable in the long, hot summer months. What we are not sure of is whether it is possible to isolate the accumulator from the system temporarily (i.e. by turning off a valve and the pump) and if so, whether it would be a sensible thing to do or whether it could lay the way open to damage being caused to the accumulator through lack of use. We would welcome any opinions, for or against, to enable us to come to an informed decision.

When you say accumulater ? I assume you mean hot water cylinder ?? an accumulater is a pressure / storage vessel for boosting the flow rate , generally found on unvented cylinder installs ????

Do your combi fire up when you turn on each hot water tap? Are you sure it's a combi?

It sounds like you have a sytem boiler/cylinder set-up. Are you sure it's an accumulator?? An accumulator would be on the cold mains side and it shouldn't be heated at all.

Here in Spain what we have is called an 'acumulador' which we translated as an accumulator. From what has been written, it looks like what we have is a large hot water cylinder which stores enough water to enable us to fill a bath without the water running cold. The boiler fires up every time a hot tap is opened and we get instant hot water. It seems also that we misunderstood what a combi boiler actually is. The installing company described the boiler as a combination boiler because it can be either just hot water or hotwater and central heating. Obviously the Spanish words, although they appear similar to the English words, do not mean the same. Sorry for the confusion.