Vaillant ecoTec Plus 428 + VRC 430 Problem

Firstly apologies for the long 1st post!

I have recently had an ecoTec Plus 428 installed with the VRC 430 weather compensator. I am having problems with the boiler constantly going into anti-cycling mode and not maintaining the required target flow temperature for more than a few seconds. Our installer didn't seem to understand the system at all well, so I'm hoping somebody can help with this issue.

The boiler appears to behave correctly when central heating is first demanded, heating to the target flow temperature issued from the VRC 430 for around 5 to 10 minutes. When the VRC 430 (which is wall mounted in the hallway) registers an increase in the room temperature and adjusts the flow temperature downwards, then the boiler seems to go into a permanent cycle as follows (VRC 430 set to 25C target room temp, actual room temp is 21.5C, outside temp 16C, heating curve 1.8, central heating set to Manual, water set to Off):

Target flow rate demanded by VRC 430 is 57C, confirmed on boiler via d.5

1. The radiator symbol on the boiler begins flashing. Status code is S.7. Flow temperature begins to drop from 57C to 43C, return temp is 43C. d.67 shows remaining anti-cycling time at 7 mins.

2. After 5 mins the pump overrun time expires (d.1 set at the default 5 mins). Status code changes to S.8. d.67 shows 2 mins remaining anti-cycling time.

3. After the anti-cycling time expires the radiator symbol stops flashing. Status code changes to S.2.

4. After approximately 15 seconds burner symbol shows, gas valve symbol shows. Status code changes to S.3.

5. After approximately 5 seconds status code changes to S.4, flow temperature increases from 43C to 57C over approximately 30 seconds.

6. Flow temperature reaches 57C/58C. After no more than around 5 seconds (sometimes less) radiator symbol begins flashing, burner symbol disappears, gas valve symbol disappears. Status code changes to S.5, flow temperature begins falling.

7. After around 10 seconds status code changes to S.7.

8. Cycle begins at 1 again.

Once this cycle has begun, it seems to continue indefinately with the boiler only reaching the target flow temperature of 57C for a 5 second maximum every 8 to 10 minutes. Clearly with this cycle the radiators cool, and the target temperature of 25C is never reached, in fact it never rises above 21.5C.

Setting d.2 to a smaller number (2 mins) decreases the time to complete the above cycle, but has no other effect on the cycle. Also setting d.1 to a smaller number (2 mins) only reduces the time that S.7 status code is shown, other than that has no effect on the above cycle. Setting d.0 to a smaller number (5kW-Max) appears to have no effect on the above cycle.

All other boiler parameters are all set to default values with the exception of d.70 which is set to 1=Centre Position.

I have tried changing the Room Temp Control setting of the VRC 430 between Off/Thermostatic/Modulating and it appears to have no effect, other than changing the target flow temperature. The above cycle still takes place. AUTO_OFF on the VRC 430 is set to ECO. Min Flow temp is set to default 15C.

I have also observed on a number of occasions when the boiler goes into the above cycle, the target flow temp suddenly changes to 0C. This causes the heating demand from the VRC 430 to be lost, boiler status goes to S.31. Displayed flow temp on the VRC 430 is then shown to be 0C, even though nothing has changed and there should be a heat demand. The only way to get the system to recover from this appears to be changing the heating curve. Upon setting the curve away from 1.8 then back to 1.8, a target flow of 57C is restored and the above cycle continues.

Circulation pump is Grundfos 15-50, changing the pump speed between the 3 available settings appears to have no effect.

Hot water and heating knobs are both set to maximum, as specified in the instructions for when using a VRC 430.

Pump seems to run as and when requested by the boiler, 3 port valve moves to the correct position controlled via VR 65 control unit.

This is driving me mad, surely it's not supposed to behave like this

Thanks!

Thats Vaillant for you

From here it sounds like you may have a lack of flow problem.

What do d40/41 read as the boiler is heating up for these 30 secs?

What is d0 set to? Could be your boiler needs range rating as it may be too big for your heating system/house.

Try setting d0 to 15 and see what happens.

Set the curve to 2.6-2.8 and try again. That is the general setting for the UK.

are you using the hot water sensor? it comes in the box with the VR65. you must use it. Set everything back to factory settings, set heat curve at about 2.3 for time being. Shouldn't need to alter any settings so dont, just makes things worse and impossible to find fault.

Hi epics.
I have what seems exactly the same problem with my boiler, fitted April 2010. I'm have the fitter coming back on Tuesday, a second visit, the first time he flatly denied there was a problem! so it's good to know I'm not dreaming up a problem.
I am cautious about making any changes to my controls until the fitter has been; don't want to give them a chance to invalidate my guarantee. Therefore, I would certainly be interested if you have had any luck with the suggestions from the other related posts.

I have written a couple of times about my problems with an Ecotec 415
and VRC430. I have minimum permitted flow and a high proportion via
the bypass. Its a very tricky setup and problems like yours very hard to avoid. Vaillant were no help and I had to work it all out myself.

A few things may be helpful. gas4you suggests you may have a flow problem. You can check this by recording the temperature rise (
subtract d41 from d40 taken at the same time (!)) when you know
what the boiler power is. This is best done from cold and after the first
minute or so but before the boiler starts to modulate down as return temperature rises. If you set d0 then you can be sure of the power
input. Now apply the magic formula (developed by myself)

Flow (litres/min) = (14.15 x kilowatts) / temperature rise

In my system. I get 13C temperature rise when the boiler is doing 10kw

Thus Flow = 14.15 x 10 / 13 = 11 litres/min approx
which is just OK for 415.

I think yours needs 20 litres/minute.

If you don't have a bypass valve then you need one and adjusted appropriately.


What you are describing is that the boiler flow temperature is very near
to target when the boiler starts. As soon as the return warms bong its
over the limit and off it goes.

On my system it is essential to not have the boiler retry until the system has cooled down enough. I have d2 set to 60! Notice that this does not mean that the anti-cycling time is 60 minutes. Its on some sort of temp
dependent curve that Vaillant wouldn't tell me about and had to work out myself. For example at target 74C it would be 12 minutes, at 65 about
20 minutes, at 45 about 40 minutes. These are the times that are actually required for cooling off. Basically set it high enough so that
the thing doesn't try to run until it can.

Depending on where your flows go, you may need to have the pump
running all or most of the time that it is anticycling.

Range rating shouldn't really be necessary as these are modulating boilers. Actually the boiler runs for the first minute without modulating.
Depending on your system, that results in a wall of hot water coming in
maybe before the system is ready to modulate. The modulating scheme is a bit slow and inflexible and can be caught out. Setting d0 to
silly low numbers gets round this problem but means that the system is
slower to heat up from cold.

High heating curves = more gas used but it may be necessary to get it to
work at all if you are not a genius tuner. I have 1.5 but I have had to more or less make it my hobby.

I have an Ecotec plus 428 with a VRC 430 and VR81 remote control unit. I woe the day I ever proposed it for my refurb and will be ripping it out for a treatment with a hammer and some concrete.

Yes, my installer might as well be putting in a hadron collider for all he knows about it, but to be fair it seems to me that these weather compensators attempt to defy the laws of physics and are never going to work.

Even if you can get the boiler to stop cycling (I can't) you are never going to get enough heat out of the radiators if it is only moderately cold outside. E.g. with a heating curve of 2.6, an outside temperature of 15C and a internal target of 20C the flow temperature is about 34C. Since when is a radiator of 34C surface temperature going to raise the room temp by 5C anytime soon?

Also, the VR40 attachment to run a hot water circulation pump does not work (after 2 vaillant engineers for 2 hours each and replacing the part).

I am long past giving a stuff about efficiency, I just want a warm house and controls that get on with it by themselves.

Disconnect your weather compensator - they are the 'in' thing at the moment, they are great for commercial applications but for domestic installations without proper insulation.etc are CARP. Room or load comensation is another alternative, but good old none is best!

BTW D2 set to 10 not 60 (factory setting is 20)

MHOL said:

Range rating shouldn't really be necessary as these are modulating boilers. Actually the boiler runs for the first minute without modulating.
Depending on your system, that results in a wall of hot water coming in
maybe before the system is ready to modulate. The modulating scheme is a bit slow and inflexible and can be caught out. Setting d0 to
silly low numbers gets round this problem but means that the system is
slower to heat up from cold.

Click to expand...

When I see a statement like that I think of all the people who read these forums without much detailed understanding of heating settings.

I agree that range rating is not needed but ONLY when the boiler has been matched to the property heat loss.

BUT many of the installations we read about here have a totally oversized boiler because many think a more powerful boiler is better. In reality its less efficient and can give rise to warm up problems because it spends too much time in the anticycle off mode. ( Hence setting it to a low figure ).

I cannot imagine a situation where a properly set W/C would not operate well in a house which is reasonably well insulated for its style.

Tony

MrFreezing said:

Even if you can get the boiler to stop cycling (I can't) you are never going to get enough heat out of the radiators if it is only moderately cold outside. E.g. with a heating curve of 2.6, an outside temperature of 15C and a internal target of 20C the flow temperature is about 34C. Since when is a radiator of 34C surface temperature going to raise the room temp by 5C anytime soon?

Also, the VR40 attachment to run a hot water circulation pump does not work (after 2 vaillant engineers for 2 hours each and replacing the part).

I am long past giving a stuff about efficiency, I just want a warm house and controls that get on with it by themselves.

Click to expand...

If the minimum heat output from the boiler ever exceeds your needs then it will cycle. Many (most?) houses are going to need less than 5kw at some time in the year. Mine often need less than 1kw. So cycling needs to be effective. One of the very silly red herrings thrown up by Vaillant engineers was that the boiler needs to keep going all the time and should be sized to match.

There is a minimum temperature setting on C9 in the "code enabled layer". I have set mine to 45C below which the boiler will always try to start up before the system is cool enough.

Setting a higher heating curve is good for a system which can respond rapidly to increased room targets. But beware that the boiler chooses a smaller anti-cycling delay and this can still result in getting stuck in a cycling loop. My objections were that it was inefficient and still didn't work.

I needed to set d2=60 to get round that. My system easily maintains steady room target. I take special measures to handle the morning and unusual heatup requirements.

Re above post, its amusing that a home owner can spend a bit of time reading experimenting and then end up knowing more that probably 90% of those who regularly install Vaillant boilers.

Based on what I see and what I read on here most installers dont even think of range rating any boilers. This partly comes about because BG seem to teach their trainees that modulating boilers dont need to be range rated.

The Vaillants have a very comprehensive set of diagnostic readings and settings but only a very few installers know much at all about them.

Tony

Beerlover said:

Disconnect your weather compensator - they are the 'in' thing at the moment, they are great for commercial applications but for domestic installations without proper insulation.etc are CARP. Room or load comensation is another alternative, but good old none is best!

BTW D2 set to 10 not 60 (factory setting is 20)

Click to expand...

My house has good insulation and I have radiators sized to work with low temperatures. Even so I have all kinds of difficulties. In my opinion the design of the boiler and controller is the problem. The Vaillant boiler starts up at 12kw and my house can't sink that. The designers have either not anticipated it or failed to adequately respond.

I think most or all of the smaller condensing boilers have burners with the same problem. I think that the industry knows all about it and isn't talking, leaving installers and users to struggle.

If the factory setting of 20 isn't good, then what would be better about 10? For me 60 works best. Vaillant engineers wanted me to try 3 minutes. Total waste of time. d2= small means that the boiler tries to restart often, so it runs as soon as it cools off enough but will have failed restarts aplenty. In my house the extra heat put in by the failed starts seriously delays the cooling so that in the worst case it may never start.
It depends on the volume in the radiators/pipes and the proportion of flow going round the bypass and not through the rads.

Given the kit, then maybe you are right and it is all a lot of BARBEL and best left alone.

Agile said:

MHOL said:

Range rating shouldn't really be necessary as these are modulating boilers. Actually the boiler runs for the first minute without modulating.
Depending on your system, that results in a wall of hot water coming in
maybe before the system is ready to modulate. The modulating scheme is a bit slow and inflexible and can be caught out. Setting d0 to
silly low numbers gets round this problem but means that the system is
slower to heat up from cold.

Click to expand...

When I see a statement like that I think of all the people who read these forums without much detailed understanding of heating settings.

I agree that range rating is not needed but ONLY when the boiler has been matched to the property heat loss.

BUT many of the installations we read about here have a totally oversized boiler because many think a more powerful boiler is better. In reality its less efficient and can give rise to warm up problems because it spends too much time in the anticycle off mode. ( Hence setting it to a low figure ).

Tony

Click to expand...

The thing of it is though that I got the smallest boiler with the lowest "modulates down to" figure I could get. I got Vaillant for reputation and credibly documented controls. I often need less than 1kw heating in the one room of my well insulated house that I wish to heat. The main rad is super large on 10mm microbore (replaced original 8mm but larger not feasible). I expected the boiler to cycle and I never dreamed it would be a problem (old boiler in old cold house cycled all the time). The catch is the 12kw for the first minute from which all evil springs.

The other point about big boilers is that Combis are all necessarily big so maybe it should be that whatever size of boiler it should modulate low. The 428 is big but can modulate as low as my 412. If it could start at that level and "feel its way up" then there would not be a problem.

You have correctly predicted much of how boiler makers design and test their boilers and apply the various parameters.

They assume a fairly standard installation perhaps equivalent to a UK three bed semi. When the design is complete they then modify it to provide the smaller and larger output variants.

When I highlighted a problem with a boiler the maker replied that they only tested them on a standard ( short ) flue and so the problem would not have been noticed on the production test.

When the Icos/Isar were introduced, I had one that had the wrong mixture on low power. It turned out that their test ran them on full power and tested that they modulated but did NOT actually test them on minimum power.

There are other threads which have highlighted the problems caused by Vaillants lighting near to full power and then running for a full minute at a fixed high power which results in the flow rising too rapidly and turning the boiler off.

Unfortunately they dont make that parameter available for adjustment.

If you were to ask the designer why not then they would probably answer that its important to heat up the combustion chamber quickly to keep NOX emissions to a low value.

Well that may be the case but it also precludes installing the boiler on a low water content system and getting good results.

Tony