Vaillant 418 To Replace Suprima 50 Heat Only

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Having my old suprima 15kw replaced next week for a new Vaillant 418 boiler.

Getting a bit worried with lots of post about problems with this boiler.

The system is 15 yrs old and is going to be power flushed before the new boiler is hung.

Lots of the problems seem to be around "circulation" I have a pump in the airing cupboard which is a Wilo Gold RS50 - 5m head. (date stamped (05/10). The pump is on setting 3.
I live in a 4 bed detached house with 11 rads (10 singles/1 double rad).

Will it pay to upgrade the pump to a 6m head? are there any other things to bear in mind?
 
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I'll let the professionals speak in more detail, but the problem on my system is sorted for now. It was caused by a slug of cold water entering the boiler, cooling the return thermistor. The boiler would go into S.53 before the cool water reached the flow thermistor, as the difference between the two thermistor temperatures was too great. It was definitely not a low flow problem.

My workaround for now is to restrict the DHW gate valve causing the auto bypass to lift and mix a little of the hot water from the flow pipe into the return. I am sure it will function quite OK with it set like that. So the problem was indeed caused by me not fully understanding the 418's software.

I've had no other problems with it in many years so I still think that it is a very good boiler.
 
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I personally would be replacing a wilo any way if Im fitting a new boiler. I would use a grundfos 15-60 should be enough for the set up your describing.

These are good boilers, but they are heat only boilers, meaning most of the work is done by your system, this unit will just heat whats passed through it. Its therefor important that the system is set up correctly.

you need a minimum of 13 liters of water being pumped through the boiler any time its in use, less than that and you are working outside the spec of the boiler and could be liable for problems.

if you have an old cylinder this might cause boiler cycling/noise issues (on any modern boiler) as old cylinders are not designed to transfer heat at the speed a new boiler will be.

Make sure (if your keeping the system open ie: your small tank still in loft) that the open vent and cold feed at set up correctly, the system is properly cleaned, ideally a filter fitted, an auto bypass valve would be needed and set up correctly.


Sounds like a lot, but when an installer fits a heat only boiler, its their responsibility to ensure the system is suitable for it, and I can promise if you've been reading about problems with these boilers, that they will 99% have been fitted wrongly to begin with.


s.53 is that the temperature difference between the flow and return temperature sensor is to great. This can only happen if the water is not getting pumped through the boiler at the correct minimum rate, (or if someones been playing about with the boiler causing it to over gas but I've never had that myself) Its the reason for the slower flow rate that needs to be addressed whether it be a pump that's too small, restrictions in the water circuit its pumping round, or a blockage building up in the heat exchanger.
 
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s.53 is that the temperature difference between the flow and return temperature sensor is to great. This can only happen if the water is not getting pumped through the boiler at the correct minimum rate, (or if someones been playing about with the boiler causing it to over gas but I've never had that myself) Its the reason for the slower flow rate that needs to be addressed whether it be a pump that's too small, restrictions in the water circuit its pumping round, or a blockage building up in the heat exchanger.

I agree that in most instances the 400's problems are probably caused by low flow, and indeed I changed from a 15/50 to a 15/60 to solve the problem of the boiler over-modulating and going into short cycle. However I believe the software in the boiler reacts too quickly to a slug of cold water entering the boiler, and if it allowed a second more before going into S.53 this problem would not have reared it's head. (Edit: If the boiler would try ramping up again after cutting back to minimum output, also there would be no problem).

Also, I don't know whether it was aimed at me, but I do not 'play' with gas carrying parts or anything that could affect mine or others safety. Indeed the boiler was FGA'd a few months ago and I checked the gas rate myself as part of the fault finding process last night. It was within tolerance (slightly on the low side actually).
 
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I personally would be replacing a wilo any way if Im fitting a new boiler. I would use a grundfos 15-60 should be enough for the set up your describing.

These are good boilers, but they are heat only boilers, meaning most of the work is done by your system, this unit will just heat whats passed through it. Its therefor important that the system is set up correctly.

you need a minimum of 13 liters of water being pumped through the boiler any time its in use, less than that and you are working outside the spec of the boiler and could be liable for problems.

if you have an old cylinder this might cause boiler cycling/noise issues (on any modern boiler) as old cylinders are not designed to transfer heat at the speed a new boiler will be.

Make sure (if your keeping the system open ie: your small tank still in loft) that the open vent and cold feed at set up correctly, the system is properly cleaned, ideally a filter fitted, an auto bypass valve would be needed and set up correctly.


Sounds like a lot, but when an installer fits a heat only boiler, its their responsibility to ensure the system is suitable for it, and I can promise if you've been reading about problems with these boilers, that they will 99% have been fitted wrongly to begin with.


s.53 is that the temperature difference between the flow and return temperature sensor is to great. This can only happen if the water is not getting pumped through the boiler at the correct minimum rate, (or if someones been playing about with the boiler causing it to over gas but I've never had that myself) Its the reason for the slower flow rate that needs to be addressed whether it be a pump that's too small, restrictions in the water circuit its pumping round, or a blockage building up in the heat exchanger.

Many Thanks for the comprehensive reply its greatly appreciated.

I will proberly go for a Grundfos Alpha 2L 15-60 as this seems to be the one now that replaces the normal 15-60.

Will it have the same distance between unions as my current Wilo?

Thanks Again

Merry xmas
 
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Can anyone help my grants vortex 26e is working the heating ok but no hot water.pipes are hot one side of pump ?
 
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You might try starting a new topic (please), rather than tacking on an unrelated query on a thread about Vaillant 400's.
 
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Thanks for the thanks, Planemad! :)

lol cheers - I know that most errors are install related but I also cannot help thinking that this can also be a failure on the part of Vaillant.
This is the difference between being good and world class if their systems are overly fussy as in essence their product has to be fitted to many combinations of layouts.

Mine is a 2013 model (Oct 13 production) so hopefully has all the latest tweaks during production that have caused problems to other posters.
 
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