Vaillant VRC 430f cycling issues - a solution?

[Modokon]

This may be of interest to those who have cycling issues using this system.
I have a VRC430f, VR61, Ecotec 428 and an Aurastor unvented cylinder.

Cycling: Mainly this occurs due to the heat flow temp being low e.g. 43C but the boiler heating past that very quickly as it turns on and then cycling off. Rinse & repeat until you tear your hair out.
I have posted in the past about this and tried just about everything, including having Vaillant's most senior regional engineer in. It's better but still not right. Not now cycling from cold, but when near the target setpoint, it misbehaves.
I'm not a gas fitter, but have picked up a fair bit about systems. I think it's just poor programming by Vaillant on the controller.
There is something that worked for me:
-I downrated the boiler to 18Kw, which should suffice even on my 20 radiator system unless it's very cold.
-Then, the key change was to set the minimum flow temp to 50C (you could even do 55C). It's screen C9 on the 430f. I took my heat curve down from 4.0 (my previous way of getting a high flow temp to try and minimise cycling) to 2.3. Now the boiler doesn't get the off signal so soon and the rads actually have time to heat up. Sounds counter intuitive as the VRC430 takes a temp and "compensates" but this works.
Worth a try if you are stuck.

 

[David937]

I'm now running a VRC430f with my Ecotec 937.

Works quite well, curve set accordingly and minimum flow temperature at 50ºc, past day or two it has been on and only cycled about once just as the house reached 20ºc. I think I'll just leave it now to do it's thing The weather has warmed up a bit now so no need for heating now.

It's set to Thermostat ATM, I could try Modulating but I don't want to upset it!

 

[Modokon]

I'm now running a VRC430f with my Ecotec 937.

Works quite well, curve set accordingly and minimum flow temperature at 50ºc, past day or two it has been on and only cycled about once just as the house reached 20ºc. I think I'll just leave it now to do it's thing The weather has warmed up a bit now so no need for heating now.

It's set to Thermostat ATM, I could try Modulating but I don't want to upset it!

I'm not too sure what the modulating does if you have the 430f thermostat providing the demand requirement for the heating appliance??? Surely the boiler would modulate accordingly anyway?

 

[David937]

I'm now running a VRC430f with my Ecotec 937.

Works quite well, curve set accordingly and minimum flow temperature at 50ºc, past day or two it has been on and only cycled about once just as the house reached 20ºc. I think I'll just leave it now to do it's thing The weather has warmed up a bit now so no need for heating now.

It's set to Thermostat ATM, I could try Modulating but I don't want to upset it!

I'm not too sure what the modulating does if you have the 430f thermostat providing the demand requirement for the heating appliance??? Surely the boiler would modulate accordingly anyway?

Yeah it modulates as normal anyway, apparently if its on Modulating then it can call for heat constantly even when the room has reached the required temperature, instead of switching off it would stay on at a really low flow temperature to just keep the room at a constant temperature. I could try it and see how it goes but like I said, it's all working fine now, so I wonder what, if any difference it will make.

 

[UpgradeME]

Yeah it modulates as normal anyway, apparently if its on Modulating then it can call for heat constantly even when the room has reached the required temperature, instead of switching off it would stay on at a really low flow temperature to just keep the room at a constant temperature. I could try it and see how it goes but like I said, it's all working fine now, so I wonder what, if any difference it will make.

The difference is increased efficiency... when in 'modulating' mode, the controller will tell the boiler what temp it wants the water to reach to achieve, then keep the room temp you set.

In thermostat mode, the boiler just heats up the water to the temp you set on the boiler, even if the room temp is not far away, it'll still run at high temp.

With both settings, the boiler itself will modulate the gas flow to achieve the requested water temp.

 

[David937]

Yeah it modulates as normal anyway, apparently if its on Modulating then it can call for heat constantly even when the room has reached the required temperature, instead of switching off it would stay on at a really low flow temperature to just keep the room at a constant temperature. I could try it and see how it goes but like I said, it's all working fine now, so I wonder what, if any difference it will make.

In thermostat mode, the boiler just heats up the water to the temp you set on the boiler, even if the room temp is not far away, it'll still run at high temp.

The flow temperature to be used is determined by the VRC430f, it varies according to both indoor and outdoor temps. Even in Thermostat mode.

 

[Modokon]

-snip-
In thermostat mode, the boiler just heats up the water to the temp you set on the boiler, even if the room temp is not far away, it'll still run at high temp.

With both settings, the boiler itself will modulate the gas flow to achieve the requested water temp.

That's incorrect for the Vaillant Total System. Flow temp is set by the VRC430f regardless of modulating/thermostat. The boiler controls are left on max for both water and CH as the 430f overrides it. Problem is that it is badly programmed so needs an update.

 

[UpgradeME]

Yeah it modulates as normal anyway, apparently if its on Modulating then it can call for heat constantly even when the room has reached the required temperature, instead of switching off it would stay on at a really low flow temperature to just keep the room at a constant temperature. I could try it and see how it goes but like I said, it's all working fine now, so I wonder what, if any difference it will make.

In thermostat mode, the boiler just heats up the water to the temp you set on the boiler, even if the room temp is not far away, it'll still run at high temp.

The flow temperature to be used is determined by the VRC430f, it varies according to both indoor and outdoor temps. Even in Thermostat mode.

Really? [goes off to re-read the manual] ... oops, sorry, looking at the latest manual here for the VRC430f I'm even more confused!!

It sounds like when set to "Thermostat" mode, it's reading the room temperature as well as Weather Compensation (outside temp) but I can't find any reference to any "modulating" setting? [The options for C8/HC1/Switch-on room temp are "thermostat / switch on / none"]

Have they changed the software/firmware from that in the manual? (would be interested to know how often they do!? and if it's updatable?)

 

[UpgradeME]

-snip-
In thermostat mode, the boiler just heats up the water to the temp you set on the boiler, even if the room temp is not far away, it'll still run at high temp.

With both settings, the boiler itself will modulate the gas flow to achieve the requested water temp.

That's incorrect for the Vaillant Total System. Flow temp is set by the VRC430f regardless of modulating/thermostat. The boiler controls are left on max for both water and CH as the 430f overrides it. Problem is that it is badly programmed so needs an update.

Where's the "modulating" setting on the 430f?

I have the VRT392 which is a 'newer' control and I thought the firmware was similar (with added outside temp) to mine, however, after reading the 430 manual again, it seems to be very different in how it controls the heating. (My statements above are correct for the VRT392 / VR65 with EcoTEC boiler)

Sorry for any confusion!!

 

[smokebox]

David and Upgrade

I think you are both right here in a way. My system is almost exactly like modokon's except I have an ordinary domestic vented cylinder (though quite modern and 'fast'. - actually 2)

It is clear that the VRC430 / boiler between them compute a target flow temp related to outside Temp, desired house target temp , heating curve you set, and the characteristics of the house heat loss rates. These latter it is said to learn, and improve its calculations over time - I suspect a couple of weeks maybe.

My observations suggest that in thermostat mode the boiler does want to fire up the flow temp to the computed temp, perhaps thereby raisig temps higher initially. So long as it doesn't drive you dotty it then clearly modulates itself down over a few stat cycles. Indeed this is revealed on the vrDIALOG software (great fun when you work it all out & get used to it.)

In direct modulation mode I think it still makes its first dash for the sometimes high computed temp (and all is well if this is not reached in first 60 seconds. in which case you are going on the bicycle!). It then quite sharply modulates down and adjusts a little from time to time but can hold steady for a good few hours while house gets to temp. reasonably quickly.

Either way the boiler/VR430 modulate - starting in steps on thermostat mode, and more smoothly in modulation mode - at least that is what I reckon. I have not yet done actual gas consumption comparisons or 'time to house target' observations! Somehow I think the modulation mode may be more efficient though I suspect only marginally. (and maybe slower with risk of house temp overshoot of target on really long time windows of heat?)

It is all quite new - the house has been grossly overheated, and I can't wait much longer for the coldest winter on record. You should see the berries on our holly trees!

I do think setting a high flow target does help avoid the bicycle rides on days when rads are not that cold to get through the first 60 seconds. The cost of this is enforcing a bit of waste gas initially, though the computed flow target soon takes over I reckon.

Interestingly I am not sure that reducing output limit kW makes much difference to getting through the first 60 seconds - I am not sure the downregulation applies in the first 60 seconds.

As stated, an annoying software issue.

smokebox

 

[David937]

Where's the "modulating" setting on the 430f?

I have the VRT392 which is a 'newer' control and I thought the firmware was similar (with added outside temp) to mine, however, after reading the 430 manual again, it seems to be very different in how it controls the heating. (My statements above are correct for the VRT392 / VR65 with EcoTEC boiler)

Sorry for any confusion!! icon_smile.gif

Read more: //www.diynot.com/forums/plumbi...sues-a-solution.294029/#2141284#ixzz1aK7yRPLI

There is no such thing as 'Switch on' on the VRC430f despite both the manual online and the one which comes with it mentioning such a function!

You have None/Modulating/Thermostat

Vaillant Technical helpline confirmed this is correct even though the manual says 'Switch on'

 

[The831Bunny]

The difference comes in the start up fan rpm and ignition burn time being different for an ecoTEC 600/800/900 series to a 400 series. Different fan and gas valve. This is makes the 428/38 over shoot really badly when low flow temperatures are requested by the 430/392.

Ignition rate is approx 80% of appliance full rating for 45 secs on a 400 series ecoTEC, irrespective of D.0.

 

[bell824]

831 also sound's to me the heat curve at 4.0 was originally to high!!

 

[UpgradeME]

The difference comes in the start up fan rpm and ignition burn time being different for an ecoTEC 600/800/900 series to a 400 series. Different fan and gas valve. This is makes the 428/38 over shoot really badly when low flow temperatures are requested by the 430/392.

Am I correct in assuming Vaillant use the same main board / firmware on the 600/800/900 as the 400 series? Do they have an "official" fix for this bug in the firmware? (over shoot on low flow temps); I understand there is a change that can be made by senior Vaillant engineers to fix it?

Ignition rate is approx 80% of appliance full rating for 45 secs on a 400 series ecoTEC, irrespective of D.0.

Hmm, ISTR changing D.0 on my 418 DID make a difference aurally (much lower fan/gas/burn noise) for the first xx seconds - Also I'm sure d.15 changed (but that may just have been coincidence). I calculated it to be approx 75% of my d.0 kW last year and it lasted for a few seconds (< 30) but long enough to cause an issue when low flow temps are requested.

Perhaps there's a difference in main board revisions and/or controller revisions or something else I changed?

 

[JoeMar]

831 also sound's to me the heat curve at 4.0 was originally to high!!

agreed - a 4.0 curve is way too high which could explain your cycling issues. start with a flat curve say 1.5 and adjust from there. you need to strike the right balance between the 'heating window' and heating curve.

ie: is it better to run the boiler at max on a 4.0 curve for say one hour or for 2 hours on a 1.5 curve?

last winter i had mine on running on a 1.8 curve with a 3 hour heating window in the evening and it worked perfectly.

unless you have a VR81 and VR61 installed keep the VRC430 set to 'Thermostat'