Vaillant 937 versus 42 Cdi versus Megaflow ---Pls Help...

[thameskinare]

I need a new boiler for runnig two showers at the same time. Heating is for 3 bed flat.

Does an average shower at an average temperature (good for avearge people) need 10 litres/minute? Will 937 42 Cdi work?

Many thanks.

 

[ChrisR]

COuple of small factoids which might help:
Electric showers are only about 4litres/minute
You can insert a flow restrictor so you can share the output from your combi

 

[thameskinare]

Would a normal shower be around the same? If it is only 4-5lt/minute per shower - would there be a pressure problem with 2 showers on a 42 Cdi

 

[gas4you]

Have you got at least 20l/min coming in on your cold mains and at least 3 bar pressure?

If not you would be wasting your money.

Also your gas pipe from the meter to boiler will more than likely have to be greatly increased in size.

 

[thameskinare]

Thanks. Both Vaillant 937 and Cdi42 installers think pressure and gas pipe are fine. I have to chose between the two???? I am also assuming a system boiler with 24kw + some storage scores better on quick bath fill and not so much on tap response time vs the combi. Is that correct?? many thanks

 

[gas4you]

Unless the gas meter is within about 3-6m of the combi then as far as the gas pipe size goes your installers are talking out of their preverbial

If you have the pressure and flow mentioned above, and proven by your prospective installer, then either of these two will out perfom a standard gravity hot water system.

 

[simond]

The nearest equivalent to the Vaillant 937 is Worcester's 440 Highflow.

The 42Cdi has a lower output of HW and isn't really a direct comparison to the Vaillant 937.

The 440 Greenstar also puts less of a load on the gas supply (30kW) so pipe sizing isn't so onerous. It uses a larger heatstore to deliver a similar performance to 937 for the 1st 200 litres drawoff.

After that the Vaillant is in front. But will you draw off 200 litres at a time? If not what happens afterwards is an irrelevence.

 

[meditek]

I should be very wary of the 42CDI (see my post Worcester 42CDI problem).

Before buying mine I spoke with Worcester technical support because I required a wall mounted boiler of similar performance to my Greenstar 400. They recommended the 42CDi. When I told them that the 400 was giving a 1mbar WP (20/19) drop via 22mm pipe they said I would be fine with 28mm installed.

I am not fine and now they don't want to know. They even said they had never heard of supply problems with the 42cdi - a patent untruth imho, the damn thing seems to require an industrial supply! So far we have got ours up to 17mbar WP but to get their warranty it has to be 18 mbar. At the same time they say it will work fine on 17 and that 17 will not cause any problems except the hot water may not be as hot as it could be. A neat way of copping out of responsibility for a totally unrelated fault!

 

[simond]

There is nothing wrong with the 42CDi and your problem lies with the gas transporter.

If you are not CORGI registered then your presales discussion with Worcester, is as they say on their prerecorded message, relies on the information you supply.

It is your responsibility to assess the gas supply via your installer.

It is reasonable to expect your gas meter to supply a 60kW range of appliances. If it does not, then the transporter has a supply issue. However, the relevent Government departments that advertise on the TV and radio campaining for fair deals for consumers have no QoS agreements regarding low gas pressure and flow.

So you are at the mercy of your gas transporter. It is not Bosch's fault, their boiler is well inside the realms of a standard domestic supply.

 

[meditek]

Simon, I am aware of this. I must have a duff Corgi installer beacause it seems the only way he could test the supply was to hook it up to the 42Cdi and see what happened. Should I be asking him some specific questions? If so, what?

Thanks

 

[Doctor Drivel]

I need a new boiler for runnig two showers at the same time. Heating is for 3 bed flat.

Does an average shower at an average temperature (good for avearge people) need 10 litres/minute? Will 937 42 Cdi work?

Many thanks.

Look at Ethos 54C combi:
http://www.ethosboilers.co.uk/products_54c.php

You can fit a secondary DHW circulation loop with it to give instant DHW at the taps. They sell a kit, or make it up yourself.

It gives 23 litres/min @ 35C temp rise. Buy the OpenTherm room temp controller. The Honeywell Cronotherm will do. It modulates the burner. It also keeps the DHW heat exchanger warm too (user selectable). The DHW heat exchanger is a coil of copper pipe with three small pipes inside that. The temperature sensors just clip on the pipes. It comes with an integral outside weather sensor as well.

What price? They sell between £1,200 and £1,300 inc' delivery plus VAT. They are cheap for what they are. A W-Bosch Highflow 440 goes for £1,550 and drops off in flowrate when the store is depleted. The 54C is an infinitely continuous combi - never runs out of DHW and the flowrate never drops too. Great for body jet showers, where many have to spend a fortune upgrading cylinder sizes when fitting them as they run of water quickly. These never run out. A Vaillant ecoTEC937 is like a washing machine on the wall, and can't match the Ethos 54C for output.

The Ethos has proven quality components used in other makes and models. The only unproven part not in other makes and models is the pcb.

It is cheap and is a far more cost effective solution to an unvented cylinder and you can even have a secondary circulation loop to the taps too. They make a kit, or make one up yourself. So no combi lag.

The larger 54C is 9.9 to 38.7 kW to CH and 9.9 to 54 kW to DHW. 23 litres/min @ 35C temp rise

The smaller 36C is 6.6 to 28.5 kW to CH and 6.6 to 36 kW to DHW. About 14 litres/min @ 35C temp rise

Designed in the UK, and made in Holland. They use a Giannoni heat exchanger, Grundfos pump and Honeywell 3-way valve. It is a commercial boiler downsized for domestic. The case is small too for the output.

See current thread on the Mikrofill.