Which combi for house with 2 showers...

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To avoid cycling most boilers has integral anti-cycle devices, and if you have a good timer/stat, e,g., CM67, these also have an anti-cycle function too.
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Christian McArdle wrote:

I specifically chose the Glow-worm over a Worcester because it will modulate down to 4.9kW (as will the 30Cxi; 6.6kW for the 38Cxi) and as it will be in an open plan kitchen living room I hope it will be happy to idle away on low rather than cutting in and out which is much more obtrusive than steady background noise. According to the docs the 30 (and presumably 38) ramps up the heating output rather than going in at full blast (can radiators fail from thermal shock? <g>)
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That's good. It sounds like the burner is based on the MAN boiler, which has excellent modulating properties.
Christian.
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The Glow Worm is a class act. Well in that price range it certainly is. We expect a user report on its operation.
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Tony, cam you override the load compensation control for thermal store use?
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I'd have to pass on this one: controls are limited to DHW temp and CH temp and from the docs I'm not aware of any installer settings
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Imm wrote:

The heating/system boiler may have this function. It is usually a jumper on the board.
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The gas valve is driven by a stepper motor which is just audible under quiet conditions. Hardly obtrusive but present nonetheless. The ramp up is pretty quick under cold conditions - more of a soft start really. Having said that I do like this boiler for ease of installation and its build. The condensate outlet pipe can be a bit tricky to connect to as it requires joining on to amongst the heating and cold water inlet pipes behind the valves on the mounting jig. Helps if you have someone around with small hands. Also when handling, the side panels at the bottom rear arent very well supported against bending if you need to take a rest when lifting up to hang it on the bracket, have assistance and a secure foothold on a good pair of steps. Once youv'e done one the rest are easy.
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I'm just going over the heatloss calcs for the house so I'll look at this issue in more detail
The Glow Worm appears to be the better choice from this perspective as it will go down to 6.6kW, while the Valliant is up at 11kW, strangely enough their 24kW version is 11.6kW!
cheers
David
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The Glow Worm is a more advanced design.
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David Moodie wrote:

In case it helps, I just looked up the modulation range for the Ideal Isar HE35 I mentioned before: 8.8kW - 23.4kW on the CH side.
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This info is great. So having given the matter a little thought, how about this as a solution to my original problem (2 showers, washing machine etc).
Glow-worm 38CXi condensing combi for the showers and all taps in the house.
A cheaper combi (circa 400-500) for the washing machine and central heating, ensuring of course that it goes down to (insert low enough number) kW to stop excessive cycling. I havent got a clue what that means!
This would seem to me a workable solution for about 1500. From what I understand the 38CXi will have enough ummph to give good showers and have enough in reserve for taps to go on and off without affecting the showers. Secondly the washing machine would have a good hot feed, again without affecting the showers.
Is this overkill, or too little? Is there anything I have missed or not understood so that this solution will fail?
Thanks for all the input so far.
Cheers,
Dean.
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Don't bother with the other combi. Use cold fill only on the washing machine. Modern machines use so little water that even using hot fill, they rarely actually get any hot water through the taps. Many manufacturers are dropping the hot fill ability for this reasons. Secondly, do a cost benefit analysis on having hot fill versus the 500 quid+ cost of installing a boiler.
Christian.
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On 11 Feb 2004 00:58:00 -0800, snipped-for-privacy@bluerose.freeserve.co.uk (Dean) wrote:

For that money you could have a MAN Micromat like I have (or rather the combi version. This will modulate down to very low power (about 3kW) and up to the rating which can be 76kW on the largest models (assuming you had the gas supply to run it - which a domestic one won't - top is about 60kW. They have a 45kW model.
This boiler also has low temperature outputs for UFH if you want or to run radiators at lower temperatures; 5 year parts and labour warranty, weather compensation.... etc.
.andy
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(Dean)

But complexity when zoning. using two combi's gives natural zoning. And if one is down then you still have hot water and heat in the house too. Divide and rule. Excellkent boilers no doubt, but try getting a MAN serviced, and the cost, and parts are not exactly on the shelf at your local HRPC branch.
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Not a problem. There are at least two sources of service and parts. I also checked the prices of the 6 most expensive items before purchase - I am very careful like that.

.andy
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On Wed, 11 Feb 2004 21:52:21 +0000, Andy Hall wrote:

Um.. The heat exchanger. The gas valve. The combustion fan. The PCB. The pump. Wonder what the sixth one was - Air Pressure switch, condensate drain trap? Various minor transducers?
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You have to watch the max capacity of the gas meter. They can take 212 cu foot/hr. To get the consumption of the appliance divide the BTU/hr by 1000. So 100,000 BTU/hr is 100 cu foot/hr.

I would do this. Buy two of the Glow Worm 30 kW combi's below, that gives change from 1500 and is within the gas meter range. Each has its own 22mm supply back to the meter. These boilers also modulate down quite low too.
Have a Honeywell CM67 stat/programmer control each combi. http://www.plumbworld.co.uk sell these from around 53 each - don't get the RF version. They optimise the start in the morning delaying the switch on if necessary.
Have one boiler do upstairs heating and one down giving two separate independent zones. Have one do one shower and one do the other. One do the washing machine and one the other. One do the kitchen tap one the bath, etc, Divide and rule. If two showers are being taken one does not interfere with the other, providing you a decent flow on each.
At the stop cock have three separate pipes direct after the cock. One to each combi (22mm) and one to the cold taps. Once again divide and rule. On each appliance have in-line restrictors onm hot and cold and reduce the flow to suit: washing machine, dishwasher, basins. leave the shower on full flow with an integral pressure balanced maixer Mira 314 I think the model is.
You would be able to couple each of the combi's oulets up, using non-return valves to serve the bath giving ahigh high flowrate into the bath, but the makers may not like this. Nothing wrong with it, it is just that it not what they are used to. You could join the oulets after the guaranbtee has ended. or have a wall mounted hot tap at the side of the bath (they look neat) from one combi, and the usual hot and cold taps from the other combi on etnbath itself.

. BTU's - 102.400 . kW - 30 . DHW Flow Rate - 12.3 L Per Min @ 35C . Height - 725mm . Width - 450mm . Depth - 334mm . Sedbuk Rating A - 90.3% . Built In Frost Protection . Fully Modulating
PRICE INCLUDES DELVIERY 723.80 Including VAT at 17.5%
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Personally, I think that not getting the RF version is a false economy because I am able to move the thermostat around the house to find the best position. Using a wired stat to do the same thing would mean so much disruption that it would never happen.
Of course, If you are sure that you know where you want the thermostat, and are sure it won't need to move for a while the wired version is probably OK. For the sake of 20 or so, I'd rather have the flexibility.
Neil
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This depends on your situation.

20? I thought more like 50.
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