Gas boiler recommendations Mk MCMLXVII

It looks like my Potterton Netaheat is down and, given its age, I thought I should be prepared for the visit with the fatal news. I have an old-style, fully pumped, unpressurised, Y-plan set-up.
I had a quick look and I failed to see a recent thread with recommendations. Are Vaillant and Bosch still OK? Last I checked, my local installer preferred Vaillant. I am thinking to replace like for like, so something like the Vaillant Ecotec Plus 415 looks ok to my untrained eye. Is the 615 (or 612) equally straightforward to fit, in the same configuration only that it includes the pump in it? Any other (dis)advantages for the extra 50 or so quid?
Cheers,
Kostas
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If you do not want to mess about with the rest of the system make sure you are going for a system boiler and not a combi. I have only had Bosch Worces ter boilers, a system boiler ( Greenstar) in the last house and combi in t he present and have been pleased with both.
Richard
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Their spares may not be cheap but as I've found to my advantage recently, for a fixed price deal they will replace *everything* required bar the heat exchanger for around £300. Well worth it if your boiler is well crocked as ours was.
Tim
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On Sat, 17 Jan 2015 18:09:41 +0000, Tim+ wrote:

I found the same with Worcester Bosch (about £270 I think) about a year ago!
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On 17/01/2015 17:54, John Rumm wrote:

Thanks for the answer John (and Richard and Tim). The boiler was fixed, I am pleased to say; it was the fan, which was readily available a few miles down the road.
Instaed of wasting your time straight away, I will seek answers about disadvantages of *converting* to sealed; a friend just had issues with taps and connections, but a statistical sample of one... :-) I think I have asked in the past about split-temp too but my memory is as rubbish as it's always been.
We also had a repeat of the conversation from 2009 with my local fitter about converting to combi *when the time comes*.
Cheers,
Kostas
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On 18/01/2015 22:45, Kostas Kavoussanakis wrote:

Disadvantages: its a bit harder to dose with inhibitor etc. If the rest of the system is on its last legs, then the rise in pressure might cause old rads to pinhole (however they would be close to doing it anyway). Very old lockshield valves may weep from the spindle and need repacking. Very slow leaks can be hard to find and can stop the heating system every few days due to lack of pressure. You open up a new fault category due to expansion vessel problems.
However on the bright side you get easy refilling with no airlocks. Less corrosion and less sludge buildup. No need for header tanks to overflow, freeze, leak etc, easier system flushing, quicker refills.
More here:
http://wiki.diyfaq.org.uk/index.php?title=Sealed_system_FAQ

Split temperature means that the boiler can run different flow temperatures for heating the rads and for heating the cylinder. So you get a boost in efficiency by being able to run the rads at a lower more condensing friendly temperature (also less wild room temperature swings and less expansion creaking and clicking) and can still get a cylinder of water hot enough.

Keep in mind that a sealed system does not equate directly to combi (yes most combis use a sealed system, but you can have a sealed system "normal" boiler as well)
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There are no issues with taps when converting to a sealed pressurised system. This only affects the boiler and associated systems. It doesn't raise your HW pressure to your taps. It's only if you change to a combi or an unvented HW tank that your supply pressure to your taps increases.
Tim
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I'd add to the advantages the impossibility of 'pumping over' This is the cause of many an open system requiring premature replacements through corrosion due to air being introduced.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 19/01/2015 11:09, John Rumm wrote:

Thanks John (and Tim and Dave). Mr Gasman suggested that if one replaces the lot (rads mainly, pipes as well potentially) the main cause of future problems (prior sludge build-up that the flush and magna-thingy cannot get rid of) goes away. But, just the rads, cost quite a lot of money to replace...

The slow leak problem concerns me a lot, esp if there is a chance of it happening underneath the floor: I have hard flooring everywhere and no (space for) hatches in large/most parts of the house.

I like the sound of that, and weather compensation, but I am not sure the installer will be able to set it up to make the most of these. We will see at quote time, hopefully in a very long time.

Yes, thanks for this. He is well keen on combi for some reason, that's why I brought it up.
Kostas
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On 19/01/2015 20:36, Kostas Kavoussanakis wrote:

It ought not be too difficult to flush it well enough...
http://wiki.diyfaq.org.uk/index.php?title ntral_heating_flushing
I found with the full flow of mains water directed through each rad in isolation for five mins in each direction, you could get pretty much everything out. The Fernox TF1 I fitted only collected a teaspoon of extra stuff in the six months after that,

Well there are to ways of looking at it. A slow leak with a vented system will mean lots of corrosion, and ongoing boiler problems. With a surprise visit from dry rot at some point in the future due to the slow soaking of something in a nice dark warm enclosed space.
With a sealed system, you can only dump a couple of litres worth of water out of it before you become aware there is a problem.
So one way or another you will fix the leak at some point, I know when I would rather detect the leak ;-)

Weather compensation is basically a posher form of split temperature operation where rather than setting the CH flow temperature with a knob (physical of software) on the boiler, its done in sympathy with information from an exterior temperature sensor. The boiler is then instructed to run the rads just hot enough to cope with the weather. Milder days (which add up to most of the heating load over the season in the UK) mean lower temperatures and better comfort and efficiency, and the few really cold ones cause the flow temp to ramp up. Most systems also allow you to select the amount of "ramping up" based on the thermal performance of the house - older less well insulated and draft proofed ones need more variation on the colder days than better insulated ones.

Lots of fitters are because they are easy to fit and keep the installation simple. In the right property, they will work fine and do a good job. You really need to look at your expected usage. A couple taking mainly showers etc, would find a combi excellent. A larger family with a good number of baths in the mix may want stored water to cope with filling baths quickly.
(you can even do *both* in the same system - use a combi to say heat a hot water cylinder for bath filling as well as using its hot water output to drive a shower)
Unvented cylinders and heat banks can come close to "all things to all men" with high volume and rate of delivery with mains pressure into the bargain. However they take space and add cost.
http://wiki.diyfaq.org.uk/index.php?title=Thermal_Stores_and_Heat_Banks http://wiki.diyfaq.org.uk/index.php?title=Unvented_DHW
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On 20/01/2015 01:28, John Rumm wrote:
<Lots of useful stuff snipped>
Thanks John.
Kostas
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On 16/01/2015 19:20, Kostas Kavoussanakis wrote:

If you must retain the vented system (personally I would take the opportunity to convert to sealed), then the 400 series will go in without too much fuss. However keep in mind that as with most modern condensors the system must be very well cleaned before installation or you will knacker a new boiler in short order - and Vaillant are not renowned for their cheap spares! You would need to use ebus controls if you want to take advantage of the split temperature operation.
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