Optimising Vaillant Ecotec plus 637 always cycling
- Thread starter Fireitup
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If the 6 loops are flowing 1.5LPM, total, 9.0LPM then the ufh demand at a dT of (45-31), 14C, is, 9*60*14/860, 8.79kw, the boiler return flow is 9*((45-31)/(65-31)), 3.71LPM. The boiler dT is, (65-57), 8C, boiler output is 8.79kw so boiler flowrate is 8.79*860/60/8, 15.75LPM, the internal bypassing is 15.75-3.71, 12.04LPM.
Check: (12.04*65)+(3.71*31)=15.75*T, T= 57C.
It will be interesting to see what you get with CH only on.
Check: (12.04*65)+(3.71*31)=15.75*T, T= 57C.
It will be interesting to see what you get with CH only on.
What is d02 on your vaillant for? I'm wondering if it's different to mine.
Mine cycles alot, I need to sort it out. I don't have ufh just 11 big rads.
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D.02 say Max. anti-cycl. time: Heating 25 min
I found this a good explanation http://vaillantcyclingproblem.blogspot.com/2012/01/anti-cycling-mode-and-d2-parameter.html?m=1
I found this a good explanation http://vaillantcyclingproblem.blogspot.com/2012/01/anti-cycling-mode-and-d2-parameter.html?m=1
You have a 438, a heat only boiler with a external (UPS3) pump and a external by pass which you have now shut off as you a have a 3 port mid position valve so a natural bypass through the rads or the HW cylinder coil when the burner cuts out or the boiler shuts down.
Your (any) boiler will cycle if the heat demand is < the minimum boiler output.
So, when you say cycling alot do you mean that it takes multiple cycles to get it to refire after the flow temperature exceeds the target temp by 5C?.
What is your target flow temperature and what is/was your anticycle tims set to?.
Do you have weather compensation or smart roostats that change the boiler target temperature?.
All this fiddling with settings is all well and good but doesn't get you away from the fact that the boiler you've got would appear to be massively over-sized for your system.
I would insist on seeing a copy of the heat loss calculations, and be seriously considering insisting the installer replaces the boiler with a 615 or 620 at their cost.
I see where you're coming from but the fact remains that a oversized boiler should still be able to heat your house or HW cylinder heating requirements even if it has to cycle, there are thousands of Vaillant combi boilers (the "8" series) that are sized for the DHW requirements so you might install a 37kw boiler to give you a DHW flow of 15LPM with a 35C rise but your heating demand may only be 15kw max and 3 or 4kw minimum. so even if a heat only or system boiler is oversized it should still be able do the necessary even if cycling. Vaillant's challenge in refiring is that they hold the ignition settings for 60 secs of up to 65% or more of the maximum output whereas other boilers do not (hold the ignition settings) and the installer/user has to try and deal with this. I don't know if this is still true of the newer Vaillants.
But this isn't a combi, and if a 37kW system boiler has been fitted to a system that only needs 12kW then the installation doesn't comply with Part L of Building Regulations. Non-compliance is a very good case for having it replaced with a more suitable model.
Interesting.
I find it strange though that the anticycle time changes (if WC installed ) or if the target temp is changed manually during any actual anticycle period, if true, it seems very poor programming, even a basic washing machine cannot change the spin speed or wash temperature once selected and switched on.
It is a very good reason if one can prove that the heating engineer/company that specked and installed it can be made to change it FOC, otherwise?
It does this
And at other times when heating has been off, it will do this to get up to temp
Is it doing that (first video) with the CH only programmed on and the roomstat calling for heat?, have the rads got TRVs?, can you post a picture of the 3 port valve and pump if close to it.
Watching that again, looks like no circulation through the boiler as the temperature rose from 36C to 70C in ~ 19 secs.
Watching that again, looks like no circulation through the boiler as the temperature rose from 36C to 70C in ~ 19 secs.
Last edited:
Yes rads have TRV
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