Worcester 42 cdi vs Vaillant 837

[webbthomas]

New to this site so please bear with me as in need of unbiased opinions ...
Currently have Baxi Combi 130 HE which has cost under £1K on repairs in the last year - time for it to go, and currently had to be switched off so no heating.
5 bed house, one bathroom (with electric shower) and ensuite shower room with mixer shower running of combi. Family of 4.

Various heating engineers have visited to quote for new boiler and all seem to be saying different causing tremendous confusion ... boiler choice seems to be centering around our "flow rate". Some measure the flow rate from kitchen tap and / or bathroom cold taps which gives a reading of 14, and the last one measured from the bath tap which gives flow rate of 19.
Some are advising system boiler only with unvented cylinder (not our preferred option as this would involve unvented cylinder in our wardrobe) whereas others say go for the Vaillant 937 ecoSTOR, WB 42 CDI or Vaillant 837.
(1) If our flow rate is definitely 14 then the latter boilers would seem to be pointless as the flow rate would not be reached, or is it accurate to measure flow rate from bath tap? Is system our only option or would the Vaillant ecoSTOR be an option - costly to run vs normal combi?
(2) Worcester or Vaillant boiler - any views on which is best.
Thanks for your help!!

 

[D_Hailsham]

Currently have Baxi Combi 130 HE which has cost under £1K on repairs in the last year

"Almost" would have been a more appropriate word - unless you were expecting it to cost over £1k. Still very expensive, whichever way you look at it,

boiler choice seems to be centering around our "flow rate". Some measure the flow rate from kitchen tap and / or bathroom cold taps which gives a reading of 14, and the last one measured from the bath tap which gives flow rate of 19.

The flow rate is important when selecting a combi boiler as it determines how much heat is required to raise the water temperature as it flows through the boiler. The standard measure is the amount of heat to raise it by 35C, e.g from 5C to 40C or 15C to 50C. A temperature of 35-40C is normally adequate for baths and showers. The heat required is directly proportional to the flow rate and is 2.5kW per litre/minute. So, if you have a flow rate of 14 (presumably litres/min), you need a 35kW boiler. A smaller boiler would mean that you would have to reduce the flow (turn the tap down) to get the same temperature rise; a larger one means that you can raise the temperature more and still have full flow rate.

Why there should be a difference in the flow from the taps needs investigating as all taps are normally fed straight off the incoming mains. Do you still have a cold water tank in the loft feeding some of the taps? A combi is fed directly from the mains, so its the flow at the kitchen cold tap which is important.

5 bed house, one bathroom (with electric shower) and ensuite shower room with mixer shower running of combi. Family of 4.

You need to think about future-proofing. How long do you intend staying in the house? Will the family grow? Will more than one shower/bath be running at the same time? If so, a combi may not be the best option as that would mean sharing the flow between more than one outlet Don't forget that hot and cold taps share the same flow; and that includes washing machines etc.

Some are advising system boiler only with unvented cylinder (not our preferred option as this would involve unvented cylinder in our wardrobe) whereas others say go for the Vaillant 937 ecoSTOR, WB 42 CDI or Vaillant 837.

A system boiler may be a better way to go for a 5 bed house (future proofing)

The installers you have contacted only seem to be considering the hot water aspect; there is the heating side to consider as well. You need to work this out using the Boiler Size Calculator. For info, a detached house has two walls front to back, a semi has one and a mid terraced has none.

You should check that the lower CH limit of the proposed boiler is as far below the calculated requirement as possible as this will make the boiler more efficient in the spring and autumn.

 

[Beerlover]

Both are good manufacturers, not a lot in it.

Personally fitted both, but a word to the wise, STAY AWAY FROM THE VAILLANT 937 - fitted three nothing but agro ! 837 fine.

Cheers