That stored water should be adequate to reheat at a leisurely rate. As the cylinder coils probaby do not absorb more that a maximum of 10 kW each then a 28 kW boiler would therefore be totally adequate.
It is not relevant what current gas assessments someone holds. It is what knowledge and experience he has. A domestic qualification can enable installation of any number of boilers up to 60 kW output each operated together.
When asking for advice its always best to listen politely to all the advice given. Its usually pretty obvious who is giving good advice!
Tony Glazier[/quote
having listened politely to your advice you seem to have made some fundemental errors in it.
firstly the building regulations dictate the time the cylinder shuld take to reheat,last time i read them it certainly didnt quote a "leisurely rate".
secondly domestic boiler qualification has been 70KW for the last 7-10years.
both trivial points, but basic problems from someone who prides himself on being above the rest of us gas herberts.
Personally my advice would be to instruct a mechanical consultant/engineer/specialist to carryout a survey and design the system from that, rather than asking varying plumbers what they think.
Best solution for you is rip them out, dependent upon incoming main size etc i'd be advising you to instal 3 X rinnai HDC1500's with a buffer vessel. this will give you 50l/m no problems.(hot water)