Worcester Bosch 42 CDI or Valiant 837 Ecotec

[Jamse1980]

Dear All

I've recently moved to a first floor Victorian era two bedroom one bathroom flat with single glazed windows etc. The boiler was unfortunately condemned prior to moving in, and so I need to replace the Potterton system boiler and an undersized tank. I'm planning on in the next two years carrying out a loft conversion which would add a bedroom and ensuite shower in the attic space.

I had two quotes for a boiler and both parties recommend going the combination route due to lack of space as a result of the loft conversion but different boilers, they are Worcester Bosch 42 CDI and the Valiant 837 Eco Tec. The systems would currently be required to supply 5 rads + towel rail and an additional radiator and towel rail with the loft conversion.

The flats is about 750 sq ft and with the loft conversion about 970 sq ft.

Can anyone advise which of the boilers would be the best bet for the flat I have at present and the extended version. The quote for the WB is approximately £200 cheaper.

Thanks in advance for all the advice.

James

 

[tonybhoy]

First off all you need to know if you have enough cold mans pressure and flow for the 42 CDI, and presumably the Valliant, You'll need about a minimum of 1.9Bar and a flow rate from the mains of around 22ltrs a minute otherwise your wasting your money and will be better off going for a lower output boiler, the 37CDI or even a 30CDI.

Another thing is the gas supply will have to be properly sized for the 42CDI and in most cases you looking at 28MM copper from the meter however this all depends on where the boiler is going to be sited, if it's going in the loft then you might be, again, better off going for a smaller output boiler.

One last thing, WB customer service is second to none so on that basis if I were choosing between the two I'd go for the WB boiler, also get a WBAI to install the boiler and your gtee will be five years on the boiler and stat if you buy a WB stat.

Tony.

 

[D_Hailsham]

Worcester Bosch 42 CDI and the Valiant 837 Eco Tec.

The WB 42CDi is the largest combi they make. It will give you fantastic hot water - provided the mains cold water flow is high enough. But it's central heating output will be about three times what you will need.

The Ecotec is also grossly oversized.


You need to measure your cold water flow rate. Time how long it takes to fill a container of known size (plastic buckets are often marked on the inside).

You also need to know the mains pressure - this will tell you if turning on a second tap will have any effect on the flow rate of a first tap. This would be bad if a bath was run while a shower ws in use.

The installer should have checked both of these before making any recommendation.

As for the heating requirement use the Boiler Sizing Wizard to find out how much is required to heat your house. YOu must deduct 2kw from the final answer as you will be installing a combi boiler. You will probably find that this will give a figure of less that 10kW.

 

[Jamse1980]

Thanks for the response, the gas pipes are 28 mm. When I queried the pressure and flow rate (gleaned off other diynot advice) I was advised that they would check when they get on site but given the area it should be ok, in hindsight perhaps not an ideal response.

 

[tonybhoy]

How can someone suggest spending the best part of £1400 on a boiler by not testing the mains pressure and flow? How do they know that your water mains is sufficient for your (proposed) new boiler?

I had customers tell me, when this issue comes up, that the other plumber (s) just puts his thumb under the tap and then tells the customer " oh, that will be fine".

I've also checked the mains flow in pressure in some areas which is perfectly ok only to find that 500 yds up the road it's completely different. Also your water mains supply pipe might be an old lead 1/2" supply pipe giving you good pressure but very little flow rate, relativley speaking, whilst you next door neighbour might have a 25MM blue poly supply pipe giving them about 30 litres a minute.

 

[Jamse1980]

Thanks Tony, I will certainly get them to check - get a new quote in!

 

[bengasman]

Supply and fit of a WB 42 CDI, provided it is done properly including thorough clean, balancing and what have you, I would expect to be looking at £2500 or more. If neither installer could be bothered to take 10 minutes and test if it would actually work, my advice would be to find a better installer; ditch them both.
I would not recommend using the WB digistat, a siemens rev24 or honeywell cm927 are both far better.

 

[tonybhoy]

I would not recommend using the WB digistat, a siemens rev24 or honeywell cm927 are both far better.

Disagree, to a point, Ben. The WB stats are the only stats that can time the pre-heat on the CDIs and are also covered by the WB warranty that comes with the boiler and can be up to five years.


Agree their not as good as the ones you mention however they are only an extra £50 which isn't that much to pay for what is in reality two timers and a room stat with up to five years warranty.

 

[bengasman]

I always turn the preheat off, so couldn't give a toss.
50 squid more than what? 50 more to add a programmable roomstat to the system, or 50 more compared to mechanical clock and stat?

 

[bengasman]

Forgot to mention, 42 cdi for a flat. Good effort.

 

[tonybhoy]

I always turn the preheat off, so couldn't give a toss.
50 squid more than what? 50 more to add a programmable roomstat to the system, or 50 more compared to mechanical clock and stat?

DT10 RF optimiser including vat =£145 odds, Honeywell CM927 inc Vat £87 or thereabouts.

WB Mechanical timer £28 + vat.

I think the preheat is excellent however you do really need to have it on a timer otherwise I agree, turn it off.

 

[bengasman]

Dunno about the preheat, it would have to be on throughout the waking hours, say 16 out of 24; is that really worth it?

 

[tonybhoy]

Dunno about the preheat, it would have to be on throughout the waking hours, say 16 out of 24; is that really worth it?

DT10 RF comes with three preset times for the preheat, don't think the times are anywhere near 16hours mate. From memory I think the first switching time is from about 7AM to 10AM then from 12 to 2PM then back on for three hours in the evening.

I think it's a great feature and use it as a selling point by telling the punter that the boiler doesn't have to fire for them to wash a dirty teacup for example whereas with my cheap Sabre 35HE it does so your talking a load of gas to wash a cup with most of it up the flue wasted.

 

[D_Hailsham]

Have you used the Boiler Sizing Wizard to check your flat's central heating requirement?

This is the amount of heat required when it is very cold, i.e -1°C. When it is warmer, you require less heat. So, if you require 12kw when it is -1°C you will only require 6kw when it is 10°C. The lower a boiler can modulate below the calculated size, the more efficient it is as the temperature rises.

The WB 42CDi modulates down to 9.4kw and the Vaillant 837 down to 12kW. As you heating requirement is likely to be about 12kW, the Vaillant is not suitable and the WB is only just suitable.

Compare that to the Broag Avanta combis, which all modulate down to 6kW. So you can choose the combi based on the hot water requirement, knowing that the heating requirement will be OK.

 

[bengasman]

Have you used the Boiler Sizing Wizard to check your flat's central heating requirement?

Boiler sizing tools, heatloss tables or mears calculators are about as useful for combi's, as french doors on a submarine; if you had ever installed a combi, or another gasfired domestic boiler, you would know that.