Weird behaviour Vaillant 470f system

[The831Bunny]

There is a version of the VR21 available in Europe that syncs with the German time signal DCF77. Not generally distributed in the UK, so I doubt you have that. Good old manual adjustment for us!

The Thermostat/modulating/none info would be good

 

[Harry Bloomfield]

There is a version of the VR21 available in Europe that syncs with the German time signal DCF77. Not generally distributed in the UK, so I doubt you have that. Good old manual adjustment for us!

The Thermostat/modulating/none info would be good

Thanks, that explains it. I did ask Vaillant UK Tech about the feature hinted at in the manual, but they didn't seem to know anything about it.

 

[Harry Bloomfield]

I have been doing a bit of experimenting, over the past few days, trying to track down the cause of this.....

If I have the night setback set at 13C day temperature 18C and override either of those temperatures by turning its knob to a higher temperature, it gives a choice of pressing OK to make the new temperature permanent, or not pressing OK which I assume should have it go back to the programmed temperatures, once the present heating period ends. It doesn't say when it should go back to normal programmed temperatures in the manual, I have assumed that it ought to work that way.

It is looking like using the HW Boost function, is at least sometimes causing the temporary desired room temperature to be stored as the default ones. I changed the HW on times, so instead of the one hour in late afternoon, it is on from 11am through to 8pm, so absolutely no need to use boost normally. It has been a little chilly on some mornings and evenings, so I have tweaked the room temperature up a little from it programmed 13C or 18C to 21C. Each time I have done that, it has defaulted back to its stored temperatures at the end of the current period. In summer I have both the day and night stored temperatures low, because its unlikely we will need much if any heating.

It would seem to be a bug in the firmware.

 

[The831Bunny]

There are three choices of how the 470 references temperature. In the installer menu>system configuration you need to check the room temperature control is set to ‘thermostat’, NOT ‘without’ or ‘thermostatic/modulating’, the heat curve is 2.4 (if you have radiators), and summer offset is -1C.

One last request for this info. It’s directly related to your symptoms.

 

[Harry Bloomfield]

One last request for this info. It’s directly related to your symptoms.

Sorry, got carried away with another issue...

It is set for 'Modulating'; Heat Curve - 1.6; Summer Mode Offset is 1K (YES 1K, not 1C)

My understanding when I set it up, was that the 'modulating' allowed the boiler to reduce its output when not much heat input was needed.

What would you advise please?

 

[The831Bunny]

Set it to Thermostat!!!

The modulating algorithm on a 470 will bring the system on with a very low flow temperature about 2-3C ABOVE the room set point. This works absolutely fine with extremely low outside temperatures over winter, however, to run the pump and boiler to circulate at circa 20-35C is wasteful and causes nuisance complaints. This is why commissioning by an experienced engineer who can adjust the many options to match the equipment to the property and site conditions is important.

Set the choice to thermostat, and the pump (if wired correctly to the boiler) will switch off after 5mins of the boiler reaching the requested flow temperature. Also set the summer offset mode to -1C. That ensures the system is off for heating when the outside temperature is one degree below the requested indoor desired temperature. You can even try -2C.

The curve needs to be 2.3-2.5 for panel radiators and a moderately insulated house, unless your radiators are very oversized. This gives a mean flow temperature of around 70C at an outside temperature of -3C. UFH correctly sized and commissioned can be 0.5-1.3.

Give that a try and you should see the difference.

 

[Harry Bloomfield]

The curve needs to be 2.3-2.5 for panel radiators and a moderately insulated house, unless your radiators are very oversized. This gives a mean flow temperature of around 70C at an outside temperature of -3C. UFH correctly sized and commissioned can be 0.5-1.3.

The radiator are 40 years old, correctly sized back when we had draughty single glazing, no CWI, almost no loft insulation and ill fitting outside doors. I have dealt with all those so the radiators are over sized some. The pump is correctly wired to the boiler.

Thanks Bunny, I'll see how it performs now.

 

[The831Bunny]

In a nutshell, radiators 40 years old ‘may’ be oversized, but temperatures for bedrooms and hallways at that time were calculated to be 18C. With 21C throughout a modern house the new ‘normal’ standard at -3C outside, you can be only just in. But with the addition of extra insulation and double glazing, you may be in the ballpark to achieve 21C. This is where correctly set Vaillant controls come into their own. The bottom line is set the curve on a freezing cold day to achieve your desired room temperature. You may get below 2, if so happy days.

One last point. Set system off mode to Eco rather than setback. That setting makes sure that the system will only switch to set back temperature if the outside temperature is below 3C, and then only after a delay of 4 hours. That stops nuisance operation of the heating overnight except in exceptionally low temperatures.

Finally, with all Vaillant appliances using ebus controls, at the boiler fascia, set the HW and heating flow temperatures to maximum. The circuits are then controlled from the 470F, unhindered by the ‘maximum limit’ of the boiler controls. A regularly missed point, not communicated very well in the UK instructions. It is on the boiler flap if you look hard though

 

[Harry Bloomfield]

One last point. Set system off mode to Eco rather than setback. That setting makes sure that the system will only switch to set back temperature if the outside temperature is below 3C, and then only after a delay of 4 hours. That stops nuisance operation of the heating overnight except in exceptionally low temperatures.

Finally, with all Vaillant appliances using ebus controls, at the boiler fascia, set the HW and heating flow temperatures to maximum. The circuits are then controlled from the 470F, unhindered by the ‘maximum limit’ of the boiler controls. A regularly missed point, not communicated very well in the UK instructions. It is on the boiler flap if you look hard though

I will have look for the Eco, I don't remember coming across it. CH & HW are both set to allow maximum boiler output temperature already - no no boiler flap, it's a cupboard model. We never need any heat over night - even when below freezing outdoors, it only rarely falls below 18C indoors with no heat input.

 

[Harry Bloomfield]

There is an interesting observation on the Vaillant boiler control systems here - http://vaillantcyclingproblem.blogspot.com/p/problem.html

It's about micro-firing, where the boiler turns on and off frequently, rather than modulating down. I don't think my system suffers this particular problem.

 

[The831Bunny]

A well documented and known issue with early OV models due to UK system design compared to European practices. There are so many variables connected to other influences like an oversized boiler and poor system design criteria. Things like pump sizing and settings, Pipe sizing, bypass settings and system balancing all contribute. This issue was addressed in later model changes, so largely this problem on a correctly commissioned system in the UK has gone.

 

[Harry Bloomfield]

One more question if I may, Bunny - as you seem to have more expertise in Vaillant's system, than Vaillant...

The 'Pump Blocking' setting default is off, might it be worth adjusting that?

I think I understand correctly, that it simply inhibits the pump (and I assume the boiler too), from restarting up, once it has stopped. The manual suggests that behaviour can auto modify itself, if the system sees the need based on relative temperatures. I would expect that setting it to a delay, would help with the micro firing, but the article I linked to suggests it exacerbates the issue so should be set to off.

What are your thoughts?