Conventional boiler or system boiler?

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Hi All,

Five years ago we had a loft conversion in our house, so the open vented CH/water system was replaced with an un-vented sealed system. This entailed removing the water storage tank from the loft, replacing the hot water storage cylinder with a sealed cylinder, and having a pump, expansion vessel etc. installed in the airing cupboard. However we kept our original boiler (an Ideal Classic NF50, which is installed in the garage).

We have now decided to replace this boiler under the scrappage scheme for a more efficient boiler. My question is, should we replace with a conventional boiler or a system boiler? Are there any advantages/disadvantages to either approach with regards to our current installation?

My understanding is that if we went the conventional condensing boiler route then it would just be a matter or swapping our existing boiler for a boiler such as the Vaillant 428. If we go the system boiler route, then we would be looking at a Vaillant 624 model, but would that mean removing the expansion vessel, pump etc from the airing cupboard? Although this would free up a bit of room, I guess it would make for a more expensive installation, as well as perhaps making maintenance more expensive, as it may be cheaper to replace an external pump than one built in to a system boiler.

Any opinions as to which would be the best route to go down? If there are no serious advantages going with the system boiler route then the higher capacity, and cheaper cost, of the Vaillant 428 boiler might be the deciding factors.

Thanks
Jon
 
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A heat only boiler is the best solution as you already have the pump etc. fitted.

But why do you want to fit a seriously over powered boiler?

You need about 15 kW so do you think its somehow better to fit a 24 or 28 kW ?

Tony
 
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A heat only boiler is the best solution as you already have the pump etc. fitted.

But why do you want to fit a seriously over powered boiler?

You need about 15 kW so do you think its somehow better to fit a 24 or 28 kW ?

Tony

Thanks. At the time we had the loft conversion done, the plumber said our current boiler may not be quite up to the job as he felt it was a little under-powered for the house at the time, and we also added an extra couple of radiators and a shower room as part of the conversion. It has performed OK, although sometimes takes a while to heat through the house and keep constant hot water.

We may be looking at adding a third shower (to the main bathroom), and might even look to converting the garage at some point in the future and/or adding a conservatory, so thought the extra capacity would be useful. However I may look at something around the 20 kW range
 
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This is aweful !

You dont just put a finger in the air to decide what power boiler!

You need to do two things:-

a. Work out the whole house heat loss.

b. Add up the heat output of your current rads using the current specifications which are based on a flow temperatures of 70 rather than 80 on your existing boiler.

Adding a loft conversion often reduces the heat requirement as they usually have lower heat loss than a poorly insulated loft.

Tony
 

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