Vaillant VRC430 - what works and what doesn't?

[The831Bunny]

Maybe I'm missing something here. Are you having problems maintaining your property temperature to a constant level? You seem to be pre occupied with the operation of the appliance and controls and how you think it should work.

I have a modern highly insulated house using 15 radiators with a heatloss/load of 10.5 Kw. The system is very common in modern build with 10mm drops to all rads from a 22mm reducing to 15mm circuit mainly within the 1st floor. It has a fairly high resistance. With a correctly adjusted bypass and balanced system I really have no problems with the 430. With the pump overrun adjusted to suit the property it is ticking over at a very consistent 21C.

I have fitted and commisioned many WC systems in domestic and commercial situations. I have attended many more 'faulty' WC controls for Vaillant UK Ltd, only a handful are really faulty. I believe your problem is sortable, but I don't think you've had the right engineer diagnose the issue yet, if there is an issue.

Cheers

 

[Bunnyman]

MHOL no disrespect but some people r experts on some things an in this case that would b mr831 u r trying to get ur boiler to do something that no boiler will however much u **** about with it. Do u honestly think everyone is lyin to u? This may sound rude but that is not the intention , either pipe it properly an use more rads to give the boiler a chance or if u really only want to heat one room forget it an fit a gas fire!!

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• Bunnyman
• 26 Mar 2010
• 499

 

[MHOL]

MHOL no disrespect but some people r experts on some things an in this case that would b mr831 u r trying to get ur boiler to do something that no boiler will however much u **** about with it. Do u honestly think everyone is lyin to u? This may sound rude but that is not the intention , either pipe it properly an use more rads to give the boiler a chance or if u really only want to heat one room forget it an fit a gas fire!!

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• Bunnyman
• 26 Mar 2010
• 499

I think of myself as being the expert on my system. What I'm hoping will come to light is what exactly it is that no boiler will ever do so that perhaps others will not mistakenly try it and, if anyone else has, to provide some advice as to how to deal with it. If it turns out that there is a community of interest than maybe Vaillant will be more motivated about addressing it.

Actually, I think it is piped properly. I'm responsible for the design which is really just a boiler replacement with a little improvement in the shape of the 10mm to the new bigger main rad and the ABV. I used an installer I found from the Vaillant website and the installer did not warn me that the system would not work.

What you are saying pretty much mirrors stuff I had from Vaillant initially. Although main rad only was my preferred configuration, I now use the kitchen and bathroom rads which works a bit better and I don't resent the cost. Even with that and my other mods the 12kw startup is the big issue. Using the rest of the rads would be heating parts of the house I prefer cold.

Even with the limitations, now that I have got it all as sussed as it will ever be, it is a whole lot better than a gas fire.

I'm not sure that I have implied that I think anyone is lying to me as such. I do think there is some sort of story which is not being told.

 

[MHOL]

Maybe I'm missing something here. Are you having problems maintaining your property temperature to a constant level? You seem to be pre occupied with the operation of the appliance and controls and how you think it should work.

No, I did have problems in maintaining property temperature but now I have sorted them. I have only become preoccupied with the appliance and controls as that was the only way to get it to work acceptably. I have had to figure out how it should work because I couldn't find out any other way. In the beginning I only knew that the thing seemed to be always trying and failing to start. I've worked out why. It would seem from your earlier posts that you know that there is a "feature" of some of the Vaillant boilers which accounts for my issues. I suspect that this applies to other boilers as well and may be a feature of the burner and that may well be a bought in item used my other manufacturers. It seems useful to be giving this subject an airing.

 

[MHOL]

I have a modern highly insulated house using 15 radiators with a heatloss/load of 10.5 Kw. The system is very common in modern build with 10mm drops to all rads from a 22mm reducing to 15mm circuit mainly within the 1st floor. It has a fairly high resistance. With a correctly adjusted bypass and balanced system I really have no problems with the 430. With the pump overrun adjusted to suit the property it is ticking over at a very consistent 21C.

Ok, then we are getting a clearer idea of what works and what doesn't. Microbore as such isn't an issue. My 10mm drops to the main rad would seem to be fine but a question mark hangs over 8mm. I get approx 4 litres a minute through my main rad, an unknown quantity through the kitchen and bathroom rads on 8mm (TRVs permitting) and the balance through the bypass. It is the high proportion through the bypass together with the low (although within spec) flow overall that causes problems.

So your house has enough total flow to keep the temperature rise through the boiler down so that the extended cooldown period problem doesn't apply. Further, you have a high enough proportion of water being cooled through the rads so you don't suffer even if the boiler does sometimes fail to restart. So d2 isn't crucial.

 

[MHOL]

Maybe I'm missing something here.
I have fitted and commisioned many WC systems in domestic and commercial situations. I have attended many more 'faulty' WC controls for Vaillant UK Ltd, only a handful are really faulty. I believe your problem is sortable, but I don't think you've had the right engineer diagnose the issue yet, if there is an issue.
Cheers

The issues are as I described them. Maintains temperature but not responsive without bodges and manual intervention. Unreasonable amount of tuning and modification required of owner.

I have had the problem looked at by Vaillant. They have measured my system and have had the issue considered by their developers. I'm prepared to believe that they have done their best bar rewrite the software for me - which btw I have suggested they should.

I think I fully understand what the boiler and waterworks issues are - perhaps apart from the tunabilty or otherwise of the 1st minute behaviour.
The VRC430 remains more of a mystery, so please feel free to clue me in.

 

[MJN]

Excellent thread MHOL; I'm making long-term plans to replace our basic Ideal Icos with something a bit more capable (lower modulation and better flow temperature control in particular) and have got my eye on an ecoTEC 415 (maybe 615) and VR430 with weather compensation.

In particular, whilst I've got the opportunity now during a house renovation to pull cables necessary to support it all I'm trying to decide now what boiler/setup I'll opt for if/when the Icos inevitably gives up the ghost.

Your system setup seems very similar to mine so your analysis of some of the issues are insightful so thank you for sharing them.

Mathew

 

[D_Hailsham]

In particular, whilst I've got the opportunity now during a house renovation to pull cables necessary to support it all I'm trying to decide now what boiler/setup I'll opt for if/when the Icos inevitably gives up the ghost.

Does your renovation include new radiators? If so, do a heat loss calculation for each room, so you can get the correct size radiators and boiler. Download either Stelrad Stars or Kermi Heatloss Program.

If you want to make the most of weather compensation and have the boiler running as efficiently as possible the return temperature should never rise above 55C when the flow temperature is 70-75C.

This means that the radiators will produce less than the stated output, so they have to be oversized by 20-25%.

PS I hope the renovation includes improved insulation.

 

[MJN]

Does your renovation include new radiators?

My choice of words was perhaps a bit misleading. I should've really said redecoration - it's a fairly new (2007) house so the work is largely cosmetic although I have made some modifications recently to some of the radiators. It's a 3-bed semi with 11 rads totalling around 9.5kW.

If you want to make the most of weather compensation and have the boiler running as efficiently as possible the return temperature should never rise above 55C when the flow temperature is 70-75C.

Yes, that's why I'm particularly keen to get a low modulation boiler. My 15kW Icos can only go down to 8.8kW so as you can imagine it cycles fairly badly. I'm running with a flow temp of around 70C and getting a ~10C drop so not great from a condensing benefit perspective. I am assuming the limited headroom to drop the flow whilst still allowing good HW reheat performance means I'm pretty much snookered here? Separate CH and HW flow temps would be ideal (and it is my understanding that the ecoTEC offers this?) and I am hoping the weather compensation can adjust the CH flow to suit the demand actually required thus improving comfort whilst taking advantage of condensing efficiencies whenever possible.

MHOL's situation with similar low load requirements is what has got me particularly interested in his experiences with his setup.

PS I hope the renovation includes improved insulation.

Given the age/design of the house there's probably little to be done there - we've got brick and block cavities with 30mm (I think) insulation boards. The loft has 300mm insulation.

Mathew

 

[D_Hailsham]

It's a 3-bed semi with 11 rads totalling around 9.5kW.

It would be interesting to work out the actual heat loss by using Boiler Size Calculator

I'm particularly keen to get a low modulation boiler.

UK, and many continental manufacturers seek to think that 9kW is about as low as you need to go. That's because they assume the system will be controlled by the tradition on/off thermostat, not a weather compensation system.

I am assuming the limited headroom to drop the flow whilst still allowing good HW reheat performance means I'm pretty much snookered here? Separate CH and HW flow temps would be ideal (and it is my understanding that the ecoTEC offers this?) and I am hoping the weather compensation can adjust the CH flow to suit the demand actually required thus improving comfort whilst taking advantage of condensing efficiencies whenever possible.

All W/C systems, as far as I know, use a hot water priority system. When HW is being heated the radiator circuit is switched off and the boiler ramps up to full output so the water is heated as quickly as possible.

Have a look at Remeha Boilers. They support weather compensation and modulate down to 6kW.

I don't know anything about them, but Geminox (part of Bosch) make boilers which modulate very low - down to 1-10kW and 2-18kW.

 

[MJN]

It would be interesting to work out the actual heat loss by using Boiler Size Calculator

It comes out as 9.72kW.

All W/C systems, as far as I know, use a hot water priority system. When HW is being heated the radiator circuit is switched off and the boiler ramps up to full output so the water is heated as quickly as possible.

To a certain extent I always work around this anyway by avoiding any timing overlaps in CH and HW demand. The separate flow temperatures would still be of benefit however.

Have a look at Remeha Boilers. They support weather compensation and modulate down to 6kW.

Yeah I've been looking at them - the Avanta 12v/15v in particular. Very impressive, to this layman at least and I liked that it is Opentherm compatible. However my main concern is that I am somewhat hesitant to go with a manufacturer who I might struggle to find a competent installer to maintain if ever it breaks down. With all due respect and acknowledgement to the varying degrees of competency out there I don't want to let anyone other than someone with a deep level of knowledge of the boiler and its configuration anywhere near it. I figured that if I go for Vaillant I'll strike a good balance between quality and common familiarity.

Mathew

 

[dumbrill]

Can the VRC430 be setup to act as a simple programmable room thermostat, ie. not using the WC, but modulating the boiler to achieve a set room temp only?

Would your system work better if you did this? I am thinking of buying a Vaillant 618, VCR430f and VR65, but I don't want the sort of hassle you seem to be having. My thought is that dropping the WC might be a good fall-back if all else fails.

 

[D_Hailsham]

I am somewhat hesitant to go with a manufacturer who I might struggle to find a competent installer to maintain if ever it breaks down. ... someone with a deep level of knowledge of the boiler and its configuration anywhere near it.

It's a boiler, not a Rolls Royce Trent 900 engine. Any competent installer would be able to service a Remeha and diagnose/repair any faults.

 

[MJN]

Any competent installer would be able to service a Remeha and diagnose/repair any faults.

Absolutely. My issue is finding a competent installer though.

From my admittedly limited sample size of two I've failed hence I can see some advantages in opting for a make whereby even the biggest monkey might at least have sufficient capabilities to diagnose faults and issues effectively and efficiently through familiarity with the boiler in question alone. What I don't want is him flicking through the installation manual pondering over configuration settings and what they do, or relying solely on trial-and-error because he's not familiar with the nuances of that particular boiler xyz. Sure, if the fault is fundamental then I'm sure there won't be an issue, but what if it's a more subtle, say performance-related, issue?

As a customer it can be difficult distinguishing between a competent and incompetent installer until it is too late. There are few, if any, distinguishing factors that are readily observable.

Calling someone in is currently a last resort option with my current setup, however with a new boiler I have little choice given the terms of the warranty.

All said and done, however, the Avanta is still on my shortlist.

Mathew

P.S. Apologies to the OP - I've dragged this topic way OT so will continue my issues in another thread if necessary!

 

[D_Hailsham]

My issue is finding a competent installer though.

But that applies, whatever the make of boiler.

The only, minor, gripe I have with Remeha is that they do not maintain a list of installers who have been on their training course. They will give you the name of your local stockist and suggest you ask them for names of installers who have experience of Remeha boilers.

What I don't want is him flicking through the installation manual pondering over configuration settings and what they do, or relying solely on trial-and-error because he's not familiar with the nuances of that particular boiler xyz.

A boiler engineer cannot be expected to know everything about all boilers and will have to refer to the manual at some time; even if they have been on the training course. I would prefer them to refer to the manual or phone the manufacturer's tech support, rather than change components willy-nilly in the hope of solving the problem.