My son's Baxi Solo 3 70 regular (vented system) boiler sometimes fails to fire up. Gas engineer showed us the problem - the venturi is distorted so the pressure switch is not holding. He said we need a complete fan unit at over 200 pounds fitted. You can get venturis for later models. Is it possible to get just the venture just for this model - over 10 years old. You can buy refurbished fan units so you must be able to get the venturi from somewhere ?