Ecotec 630 plus economy improvements

3 Jan 2015
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United Kingdom
Hi I'm new here, hope this isn't too rambling and someone can help...

I had a Vaillant Ecotec plus 630 installed into my mid terraced, OK insulated house with 11 radiators around 18 months ago. It's generally performed fine, making big savings on the non-condensing boiler that it replaced but I've got a few questions.

Is there a way to tell when the thing is condensing?

Wondered if there was an installer parameter code that might indicate whether it is or not...

Balancing the rads

I noticed that some rads weren't getting as hot as others so decided to balance the system using an infrared thermometer. Looking through the boiler manual, I found that code d40 displays flow temperature and d41, return temperature. Excellent, I thought - this should make things easier. I then balanced all the rads no probs but the readings the boiler display gave didn't make sense - a return temp of 59c with flow temp at 65c = 6c drop! I decided to measure the flow and return pipe temperatures just before the boiler and they showed more what I expected: 63c flow and 45c return, a drop in line with what I'd achieved over the rads and also a return temp that (I hope) will allow the boiler to condense.
So is the reading of d41 faulty or am I misunderstanding what it's actually displaying?

Thermostat behaviour

The single zone CH is operated by a Honeywell DT90E Thermostat and Honeywell ST9400C controller. According to the Thermostat manual, you can set the number of 'calls' per hour the thermostat makes to the boiler to achieve the desired temperature. At the moment it's set to 6 per hour ( default). When the desired temperature is reached, the demand goes off and the boiler goes into lockout (anything between 2 and 4 mins) with the pump on overrun (set to 5 mins). Once the lockout time has passed, and if there is demand, the boiler kicks in again but seems to burn very low around 48c for a few minutes before finally firing up to full blast and 65c target flow temperature, for a couple of minutes max. Then another 10 min 'call' is up so the whole process starts again.
I've read in a few places that the fewer calls to the boiler the better, so would setting it to 3 per hour make sense?
Should I look at adjusting the boiler pump overrun or lockout times at all? I wondered if making these longer would allow the system to just pump the already heated water around, operate in what I think is condensing mode for longer and maybe miss the full firing cycle towards the end of the 10 minute call window?
I've read that Vaillant make room thermostats (VRT50) that are continuous and modulate the burner. Would one of these cut out all the boiler lock out/firing up activity? I think they only run via the Vaillant ebus system so would have to buy a new timer and VR66 to make all that work which seems quite an outlay...

Heating Partial Load setting

Parameter d0 is currently set to 30kW. I have 11 rads plus a hot water tank, so does this setting really need to be so high? What would be a good figure to change it to, or does the 'auto' setting do a pretty good job of getting it right?

Thanks in advance to anyone who can take the time to help answer theses. I've spent a good few weeks trawling the web but not been able to find answers and the installer pretty much setup it up and left without really explaining (or balancing) the system very well.
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Not much you can do with it to be honest. 30kw boiler sounds very oversized for your house so burner cycling will always be an issue.

Out of curiosity is it an older vented or newer unvented cylinder you have for the hotwater?

you can use the modulating controls but you are correct in saying you would need to use the Vr66/Vr61 and Vaillant ebus controller set for hot water priority mode.

Without know the exact heat loss from the house its impossible to say, but I'd bet a 15 or 18kw system boiler would have been more than enough and would run more efficiently without cycling.

As far as condensing goes, it wont make much difference to the bills, youve already made the big difference by using a high efficiency boiler, you would want to set your flow temp to 50 or 60 degrees to increase the time spent in condensing mode (of whcih there is no indicator) but that may not be hot enough to heat the house depending on radiator sizes
Cheers for the quick reply ScottishGasMan. It's an older vented cylinder which seems to do the job OK - got the thermostat on that set to 60c.

Just as I thought re. ebus. Reading up on it I think I'd also need to get a Vaillant timer/controller too?

You mention a smaller system boiler - if I set the partial heating load setting to something around 15 or 18kw as you say instead of 30kw, would that make a difference to the cycling?

Using I get a figure of 8kw which seems quite low....
Prob not a million miles away, and an older style cylinder will only use a max of about 4kw typically, so really a 15kw boiler would have been most efficient, certainly set d0 to 15 and see how it runs, but a larger boiler (30kw) can not modulate the flame as low as a smaller one meaning once it's approachting set temp it will still cut off and cycle more frequently
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Will give it a go and post results in a few days, cheers.
Another example of "Spinal Tap" specification.

For your reference OP - I have a 4 bed detached mid 80's house. Heatloss is around 11 or 12kW.

I have a 15kW boiler that spends a large chunk of its time cycling.

Well, after a couple of weeks mucking about, I'm none the wiser. The boiler seems to get the heating job done quickest when running at full power of 30kW and doesn't seem to cycle too much. I set the pump overrun time to around 12 mins so that in the 'down cycle' time of the the thermostat the hot water in the rads is still being circulated. This seems to stop the thermostat demanding more heat quite as much and hence less cutting out which I figure must be good.

Happily, gas consumption doesn't seem to be affected whether it's running at 18kW or 30kW but I guess that goes with what others have said about only being able to 'downrate' a big boiler so far...

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