Vaillant VRC 430

[epics]

Hi,

I have recently had a Vaillant VRC 430 + ecoTec Plus 428 installed and all seems to be working OK except for one problem.

The VRC 430 flow temperature demand is changing to 0 degC for periods of around 10 minutes when the radiators should be heating up. Obviously this delays the warmup of the radiators quite significantly and this happens several times during a heating period. It happens when the actual room temperature is below the target room temperature. The unit is wall mounted. After around 10 minutes or so at 0 degC it recovers and goes back to the flow temperature corresponding to the selected heating curve.

Does this sound like a faulty unit, or is this a 'feature' of the VRC 430?

Thanks

 

[MHOL]

In my reply to your previous post, I said that I have d2 set to an unfashionably high value on the basis that the boiler must not try to start until the return water is cool enough so that the temperature rise produced by the 12kw start up rate. Up to this point I had never seen the VRC430 switch the boiler off unless target temp had been reached.

With my new settings ( and other mods described elsewhere ) the boiler
pretty much never tries to start unless it can. However I have also noticed that the VRC430 is now doing what you describe under some circumstances.

For example:

I'm trying to get a max heat up after being out. I disable WC by setting the minimum temperature to 74. From previous extensive experiments I know that the boiler would attempt to retry after 12 mins if VRC430 kept calling and temp will have dropped to 60C which is just low enough to allow restart to succeed. However the VRC430 now stops calling (target 0) as soon as the boiler cycles. It then kicks back in (at 74C) after about 14 minutes and the boiler restarts easily from about 58C. This annoys and worries me because it is wasting a few minutes and what if it tried too early? I feared that its malign intelligence might undo everything I have achieved. So far that has not happened.

My explanation for this is that the VRC430 has "learned" my system to some extent and is now making up its own mind about cycling and overriding the boiler. It certainly didn't do it before or not enough for me to notice. I think it was simply jazzed out by the hopelessness of the boilers attempts to start.

In your previous post you described a more general problem. I'm wondering what you did to improve things. Would you give us a brief summary?

 

[epics]

Sorry, I meant to update the older thread with the results of tweaking but hadn't got round to it yet.

I will post my experience here instead:

Having tweaked all sorts of settings on the boiler, including range rating right down to minimum. Also increasing the flow in the system to maximum by fulling opening bypass valve and running pump on maximum setting, the cycling problem still occurred.

I believe it is simply because the boiler starts up at full power and the very low flow temperatures that the VRC 430 demands without a large temperature differential between indoors and outdoors are very quickly exceeded causing the boiler to shutdown.

Without a very large anticycling delay for sufficient cooldown, you end up in this cycling mode with very little heating input to the house. We found this very slow warmup unacceptable and have sacrificed energy efficiency and probably defeated most of the advantages of weather compensation by setting the minimum flow temperature to a large value (currently 58 degC).

This seems to allow the boiler to fire up without exceeding the temperature and we experience a lot less cycling and a much faster heat up time.

But, the 0 degC flow temperature problem above is substantially delaying this faster heat up time. I cannot see any good reason why the controller would want to request 0 degC as a flow temperature when the boiler is quite happily maintaining the requested flow temperature.

I think we've reached the point where we're going to swap the VRC 430 for a VRT 360 programmable room thermostat. We're probably not achieving the advantages of weather compensation with a high minimum flow temperature and the other issues with the VRC 430 make it far from an ideal control solution.

 

[Agile]

Having tweaked all sorts of settings on the boiler, including range rating right down to minimum. Also increasing the flow in the system to maximum by fulling opening bypass valve and running pump on maximum setting, the cycling problem still occurred.

If you fully open nthe bypass then the hot flow will be returned to the return as hot and make the boiler turn off as the set flow temperature has been reached.

With that model the pump probably does need to be on maximum.

You should always continue your existing thread because now all I know about your system is what you have said above.

Do you really need 28 kW of heating power? Is it a six bed detached or larger?

Tony

 

[RoyMacDonald]

The boiler should modulate down to 8kw so it shouldn't matter about the size of boiler. I read here that they only have one size of that model boiler running different software anyway.

I have a VRC 430 and I've never seen that behaviour. My flow controls are set to max on the boiler as per the instructions and I have the VRC 430 set to modulating. The heating curve to 1.7

The flow temperature with an outside temperature of 13 C is 29 C to 41 C. Most of the time it is in the mid thirties. I don't know what it is at morning startup as I'm in bed. No point in having weather compensation if you're going to get up and fiddle with the boiler.

 

[RusClarke10]

As this must still be under Vaillant's 2 year warranty, get them to check this out. Try calling them directly on 0870 6060777, they should be able to help.

 

[Agile]

The boiler should modulate down to 8kw so it shouldn't matter about the size of boiler. I read here that they only have one size of that model boiler running different software anyway.

Thats not the point.

If the max power is too high the boiler will come on and within a very short time the return temp will rise and the boiler will turn off and commence the anti cycle delay.

During the anti cycle delay, no heat is being added to the system. So 2 min on and 5 off will give less heat to the system than if the boiler had been firing continuously for 7 min allbeit at a lower output power.

Even 8 kW is far more than the heat loss of an average three bed house for most of the year. Here its currently 10.2° outside and 20.9° indoors. Taking into account about 700w for the computer and TV/audio that needs a heat input of perhaps 4 kW or less.

Tony

 

[RoyMacDonald]

The boiler should modulate down to 8kw so it shouldn't matter about the size of boiler. I read here that they only have one size of that model boiler running different software anyway.

Thats not the point.

If the max power is too high the boiler will come on and within a very short time the return temp will rise and the boiler will turn off and commence the anti cycle delay.

During the anti cycle delay, no heat is being added to the system. So 2 min on and 5 off will give less heat to the system than if the boiler had been firing continuously for 7 min allbeit at a lower output power.

Even 8 kW is far more than the heat loss of an average three bed house for most of the year. Here its currently 10.2° outside and 20.9° indoors. Taking into account about 700w for the computer and TV/audio that needs a heat input of perhaps 4 kW or less.

Tony

I'm not sure what you mean by "if the max power is too high" What max power do you refer to?

The output will be 8kw unless the demand is higher and it will modulate accordingly. ie you have enough rads or underfloor circuits or big enough coil in your HW cylinder to pull heat from the system.

When the flow temperature sensor detects the heat being being taken from the system in conjunction with the outside temperature sensor and thermostat sensor and the user demand temperature, it will set a flow temperature according to the algorithms the weather compensation system is using.

This is what my Danfoss BEM 4000 used to do and the Vaillant weather compensation system is even more accurate. I'm getting the house temperature accurate to within 0.2 C.

 

[MHOL]

As this must still be under Vaillant's 2 year warranty, get them to check this out. Try calling them directly on 0870 6060777, they should be able to help.

My system (small house - low flow) doesn't work very well. Vaillant initially tried to shrug the matter off but later took it more seriously. I did a lot of work to explain the problem to them and made a formal complaint.

Eventually they came up with this:

"Following an investigation and discussion with R&D into the issues you have raised I can confirm that as the system demands too low an output from the boiler and unless a buffer store system is used in conjunction with the boiler this problem is likely to remain.

... (re my many suggestions for solutions) ... In addition to this, we do not believe that there is a gas boiler product in the Market at present which will perform to your specific requirements."

Now I have the required minimum flow through the boiler and it doesn't specify anything about minimum heat flow in the docs for the boiler and
controller. It seems a bit sad that I could have bought a solution that wasn't. Perhaps they should have been "up front" with the limitations?

Clearly they can deny responsibility so I wouldn't be all that optimistic about Vaillant's helpfulness.

 

[RoyMacDonald]

As this must still be under Vaillant's 2 year warranty, get them to check this out. Try calling them directly on 0870 6060777, they should be able to help.

My system (small house - low flow) doesn't work very well. Vaillant initially tried to shrug the matter off but later took it more seriously. I did a lot of work to explain the problem to them and made a formal complaint.

Eventually they came up with this:

"Following an investigation and discussion with R&D into the issues you have raised I can confirm that as the system demands too low an output from the boiler and unless a buffer store system is used in conjunction with the boiler this problem is likely to remain.

... (re my many suggestions for solutions) ... In addition to this, we do not believe that there is a gas boiler product in the Market at present which will perform to your specific requirements."

Now I have the required minimum flow through the boiler and it doesn't specify anything about minimum heat flow in the docs for the boiler and
controller. It seems a bit sad that I could have bought a solution that wasn't. Perhaps they should have been "up front" with the limitations?

Clearly they can deny responsibility so I wouldn't be all that optimistic about Vaillant's helpfulness.

I'm interested to know in what way it doesn't work very well.

The flow is heated according to the desired flow temperature and circulated at that temperature with TRV's turning off rads as room temperature is reached. That's how my rads work so at some point the boiler is heating just the towel rails which I have plumbed in open circuit. The demand from two towel rails in October with weather compensation is tiny and the flow temperature can be as low as 31 C yet my Vaillant 24k system boiler manages fine just heating just enough to maintain comfortable temperatures.

I don't see how the load however small is relevant to how the system works with a weather compensated modulating boiler, and if it was such all systems would have problems when their TRV's started shutting down.

I had a non modulating condensing system boiler installed previously with a Danfoss weather compensation system and that worked fine as well.

 

[MHOL]

I'm interested to know in what way it doesn't work very well.

The flow is heated according to the desired flow temperature and circulated at that temperature with TRV's turning off rads as room temperature is reached. That's how my rads work so at some point the boiler is heating just the towel rails which I have plumbed in open circuit. The demand from two towel rails in October with weather compensation is tiny and the flow temperature can be as low as 31 C yet my Vaillant 24k system boiler manages fine just heating just enough to maintain comfortable temperatures.

I don't see how the load however small is relevant to how the system works with a weather compensated modulating boiler, and if it was such all systems would have problems when their TRV's started shutting down.

I had a non modulating condensing system boiler installed previously with a Danfoss weather compensation system and that worked fine as well.

I hope you don't mind that I'm using this to start a new thread "Vaillant VRC430 - what works and what does not?" citing you as an example of a happy customer in contrast with myself.

Please see the new thread for a description of my problem. I would like also to reply to you personally. I'm thinking that you ought to have the same sort of problems as I have and I'm intrigued that you don't. The TRV's all closing issue would surely apply to others but I suspect that it may be more usual to have the radiators in some "main room" controlled by a thermostat (such as the VRC430) and without TRV's. If most most of the flow goes through those radiators then I would not expect there to be a problem. My first ever central heating was all TRVs with a bypass and it worked fine.

You say your boiler is a system boiler. Would it be the Ecotec 624? So that has it's own built in bypass valve and pump? It is possible that the system boilers do something different or the VRC430 works better with it.

On my boiler modulation is from 5 - 15 kw but crucially the boiler starts at a fixed 12KW and can't modulate for the first minute. With my flow that gives a rise from return to flow of 16C. When the boiler tries to restart after cycling it can only do so if the return water is more than 15C below the target. If the boiler tries to restart and fails, the extra heat in the flow round the bypass impairs further restart attempts and it can get stuck cycling. I have my boiler set to maximum anti-cycling delay (60 mins at 20C as they say) and that avoids failed restarts but only down to a flow temp of 45C so I have that set as a minimum in the VRC430. As stated earlier, there seems to be some involvement of the VRC430 in taking over control of cycling. It didn't do that in the early days when I was always having problems but kept calling for heat which left the boiler to always stupidly try to start too early. My working assumption is that the VRC430 has "learned my system" and is now making its own decisions. I find this rather worrying.

Some possibilities:

1. The burner on your boiler starts at a lower level. If so I will be hassling Vaillant to replace mine.

2. You have a lot more flow and therefore a lower temp rise in the boiler.
However, if much of the flow is just around the bypass, then there can still be a problem because the boiler may during the first minute be getting water back which has already been heated.

3. The VRC430 does the anti-cycling and is doing a lot better job in conjunction with the system boiler. Mine seems to be doing that now
but always used to just keep calling for heat and left that to the boiler. If your system never worked as badly as mine used to then perhaps it could learn your system.

4. Are your radiators on 15mm pipes? I'm thinking that microbore could be a key component of my problem.

I would be agog to hear any more observations about what your boiler does at startup especially if is restarting after cycling while the thermostat is calling.

I'm hoping that my other thread will help to explore the parameters for success.

 

[RoyMacDonald]

[quote="MHOL";p="1774480

I hope you don't mind that I'm using this to start a new thread "Vaillant VRC430 - what works and what does not?" citing you as an example of a happy customer in contrast with myself.

Please see the new thread for a description of my problem. I would like also to reply to you personally. I'm thinking that you ought to have the same sort of problems as I have and I'm intrigued that you don't. The TRV's all closing issue would surely apply to others but I suspect that it may be more usual to have the radiators in some "main room" controlled by a thermostat (such as the VRC430) and without TRV's. If most most of the flow goes through those radiators then I would not expect there to be a problem. My first ever central heating was all TRVs with a bypass and it worked fine.

You say your boiler is a system boiler. Would it be the Ecotec 624? So that has it's own built in bypass valve and pump? It is possible that the system boilers do something different or the VRC430 works better with it.

On my boiler modulation is from 5 - 15 kw but crucially the boiler starts at a fixed 12KW and can't modulate for the first minute. With my flow that gives a rise from return to flow of 16C. When the boiler tries to restart after cycling it can only do so if the return water is more than 15C below the target. If the boiler tries to restart and fails, the extra heat in the flow round the bypass impairs further restart attempts and it can get stuck cycling. I have my boiler set to maximum anti-cycling delay (60 mins at 20C as they say) and that avoids failed restarts but only down to a flow temp of 45C so I have that set as a minimum in the VRC430. As stated earlier, there seems to be some involvement of the VRC430 in taking over control of cycling. It didn't do that in the early days when I was always having problems but kept calling for heat which left the boiler to always stupidly try to start too early. My working assumption is that the VRC430 has "learned my system" and is now making its own decisions. I find this rather worrying.

Some possibilities:

1. The burner on your boiler starts at a lower level. If so I will be hassling Vaillant to replace mine.

2. You have a lot more flow and therefore a lower temp rise in the boiler.
However, if much of the flow is just around the bypass, then there can still be a problem because the boiler may during the first minute be getting water back which has already been heated.

3. The VRC430 does the anti-cycling and is doing a lot better job in conjunction with the system boiler. Mine seems to be doing that now
but always used to just keep calling for heat and left that to the boiler. If your system never worked as badly as mine used to then perhaps it could learn your system.

4. Are your radiators on 15mm pipes? I'm thinking that microbore could be a key component of my problem.

I would be agog to hear any more observations about what your boiler does at startup especially if is restarting after cycling while the thermostat is calling.

I'm hoping that my other thread will help to explore the parameters for success.

[/quote]
I don't monitor my boiler much now as it all seems to work OK but when I did originally the flow temp was similar to the ambient air temperature at start up rising quickly to the weather compensation calculated flow temperature of 31 C. It then cut off the heat and just ran the pump for quite a long time until the flow temp fell to about 24 C then heated it back up to about 35 C and then off and so on. This was at the beginning of the month. The burner only comes on when the flow temperature drops to whatever it decides is the minimum. That rises as the external temperature drops. It typically is running at 50 c dropping to 45 c with the outside at 1 C this morning. I have a night setback temperature of 17 C but you need to look at the rest of my system detailed below as parts of it are on all night at a lower temp.

The boiler starts at 8 kw and goes up to 24 kw When it very first came on the installer said it was running at 8 kw and he couldn't test it for any other output because of the weather compensation and the warmth of the weather. June (even with the special test setting)

You are correct it is a Ecotec 624 plus. So yes it has a built in bypass. However my towel rails are plumbed in open circuit as my previous boiler had no bypass and I like the towel rails to be hot all the time. Which they are, to varying degrees according to the weather compensation temp the system is running.

The VRC 430 will be running heating curves and using algorithms to decide the characteristics of your heating system and insulation. That's what you have paid for so you don't have to worry about adjusting the boiler and stats. (theoretically anyway

My system is a little unusual in that the VRC 430 is running just the radiators in theory anyway. They all have TRV's. They are all plumbed in 15 mm branched from 22 mm from 25 mm from the boiler. The 25 mm splits into two 22 mm one for the heating and one for the hot water. That's all upstairs. The boiler is in the garage downstairs. Now this is where it gets unusual in that the 22 mm drops to downstairs are plumbed to my underfloor heating system manifold which covers the whole of the downstairs. The circuits to each room have their own thermostats which open and close the valves to each circuit. That system decides how much heat it wants but has no direct control over the Vaillant boiler or VRC 430 other than the weather compensation system can detect the heat load and has to compensate for it. The VRC 430 is in the downstairs hall so has no direct control via room temperature over the system as all the rads are upstairs. The underfloor stat in a different part of the hall. (the hall area is 25 m2) so quite a long way away. That's why I needed stats with a low switching differential to match the accuracy of the Vaillent weather compensation. Otherwise the underfloor pump either stays off or on for too long.

So when the system boiler was first commisioned it was in the summer and I hadn't connected the underfloor at that point so it was just the rads on TRV's and the open circuit towel rails. So basically it was just heating the towel rails at first (at a very gentle temperature) About 25 C I would guess.

That's why I don't think that the load should be a factor however small.

I'm guessing you have a combi and I'm afraid I have no experience of them. I live in a very high area an if the water is cut off ours is the first to go so I like to have nice big tanks of hot and cold to get us past the lack of supply without much of a hassle. Been a lot better since they built the water ring main around London though.

Hope you can get something useful out of this.