Boiler has died - new boiler advice please. Thinking of a Viessmann

Coldandmiserable

My Keston 55kw boiler has finally given up the ghost.  Wasted £1000 repairing it before Xmas - needs more work done now as it won’t ignite - but I’m done with it.  With what I have paid out on it the last three years I could have bought two new boilers!
So looking at online reviews I’m thinking Viessmann.  House is 5 bedroom and 4 bathroom. 2 hot water tanks. 4 towel rails.  4 radiators. 13 underfloor heating zones. Do I need a system boiler? And if the old boiler was 55kw - do I need at least he same, or can I get away with a smaller kw boiler?

fatewise

Coldandmiserable said:

My Keston 55kw boiler has finally given up the ghost.  Wasted £1000 repairing it before Xmas - needs more work done now as it won’t ignite - but I’m done with it.  With what I have paid out on it the last three years I could have bought two new boilers!
So looking at online reviews I’m thinking Viessmann.  House is 5 bedroom and 4 bathroom. 2 hot water tanks. 4 towel rails.  4 radiators. 13 underfloor heating zones. Do I need a system boiler? And if the old boiler was 55kw - do I need at least he same, or can I get away with a smaller kw boiler?

 
You only need a system boiler if you plan to do away with the header tank, usually in the loft. Other issues can result from the higher pressure of a system boiler, if you are planning on retaining the remainder of the  current heating system e.g. radiators, etc.
So no, you don't need one probably.

The size of the boiler is decided based on how much heat is required to be produced. If you put in a smaller boiler, it will produce less heat.

Think of sitting in front of a 2 bar electric fire trying to keep warm, but then turning off one of those electric bars.

Sorry, I guess I'm not really following your thought process that led you to ask those questions.

Cardew

Welcome to the forum.

Oil or gas?

I have two gas Viessmann boilers, an unvented boiler(i.e. pressurised) for the main house and a combi for an annex - both with manufacturer's 10 year guarantee - and both have been excellent.

With modern condensing boilers it is a mistake to have them too large as you need to get them in condensing mode. Mine is 32kW output which is the largest of their 'standard' range. You would need to get a plumber to assess the heating requirement but I suspect 32kW would be sufficient.

Talldave

Yes you want a system boiler as a combi would be insane in that size property.

I have no qualifications in boiling sizing, but can report that the place I'm renting (5 bed, 3 bathrooms, 10 rads, 3 UFH zones and 300L tank) has a Vaillant 37kW boiler and it appears to cope perfectly well.  Maybe a 32kW would be OK - that might just depend on how good your home's insulation is - ie: how hard the heating has to work.

Dunkelmann

I have a Viessman combi boiler in a 4 bed house.  I would recommend it wholeheartedly.  I did some research before choosing, but basically it is a good design and reliable.