Vaillant ecoTec Plus 630 boiler not reaching target temp

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windsortg

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I recently had a new 2023 Vaillant ecoTec plus 630 (30kW) system boiler installed along with a Low Loss Header (LLH) in my house. I have 21 rads in the house and a room with UFH. The LLH was introduced as I was finding (before the LLH was fitted) that my old boiler (Vaillant heat-only boiler) was anti-cycling as the demand from the UFH was too low for the boiler to remain firing. This issue has gone away since the introduction of a new boiler & LLH.

I have noticed in the last couple of days that with the boiler target temp set to 65 degrees, the boiler flow temp (d.40) takes an age to get to 60+ from cold. Even when the boiler was running continuously (with just CH on) for 2 hours this morning, the boiler flow temp reached 61C (d.40), boiler return temp - 52C (d.41)

d.00 on the boiler is set to "Automatic".

The boiler displays 5 modulation levels and it is currently displaying level 2. Is there any reason on why the boiler is not reaching its target temp and/or why the boiler is not modulating at a higher level to get the boiler flow temp close to the boiler target temp ? Even now with both, CH and UFH, demanding heat from the boiler, the modulation level is at 2.

Any suggestions on why the modulation level is not going above 2 will be much appreciated.
 
How big are the rads? Could be that the boiler is undersized?
 
windsortg said:
However, if it was, why would it cause the problem I am seeing?
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If it were undersized, it would struggle to heat up efficiently. Let’s say 1kw per rad, that’s 21kw, plus ufh and dhw.
 
If the rated output of the rads is a unlikely 30kw then they will emit 19.93kw, at flow/return temps of 61C/52C, (room temp 20C)
If they are rated at a more likely say 25kw they will emit "only" 16.61kw, 55.4% of the boilers output, the boiler is only displaying level 2 on a 5 level modulation scale, or 40% boiler output so looks like the boiler certainly isn't undersized under the above radiator flow/return conditions and should have no problem in reaching its target temp of 65C.
 
From memory, my Vaillant boiler didn’t work too well when d.00 was set on 'automatic'. I’m pretty sure someone on here told me not to use that setting. Have you tried setting d.00 to the boilers maximum output?
 
Thanks @Mottie. Do you recall what issue you had before you changed d.00 ?

Since my boiler is a 30kW boiler, I assume I would change d.00 to 30? What difference can I expect?
 
windsortg said:
Thanks @Mottie. Do you recall what issue you had before you changed d.00 ?

Since my boiler is a 30kW boiler, I assume I would change d.00 to 30? What difference can I expect?
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I’m not a heating engineer and I only know from piddling about with my Vaillant. I think on d.00 it didn’t really get hot enough like yours - or did but it took ages. Mine is a heat only boiler, 18Kw, which I now have set on d.00 at15Kw. I have just 10 rads. You can also set the heating water temperature. Mine was initially set at 75°. I now have it set at 62°. Give it a try, what have you got to lose?
 
On auto the boiler reaches peak fire and then modulates to maintain temperature required as set on the front panel. If the temperature of flow rises above that, burner Shuts down for predetermined period. Setting d0 to an arbitrary number just means boiler will not ramp up to 30kw

You need to look at the system and see why the system is not sinking The heat boiler is providing
 
thanks @DP. What I am finding (and I noticed this, this morning) is that once the room stat setting has been reached, i.e. to 21.5C, the room stat sends a signal to the boiler to turn off. When the room temp drops down to 21C, it sends a demand to the boiler for heat. I noticed the boiler flow temp takes a long time to rise, and it will not go above 58C. The radiators no longer become hot.

Therefore, I am finding that the boiler is not reaching peak fire (i.e. boiler target temp of 65 degrees). d.00 is still set to 'Automatic'
 
DP said:
On auto the boiler reaches peak fire and then modulates to maintain temperature required as set on the front panel.
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Out of interest, what’s the difference between setting it on auto compared to setting it on the max KW of the boiler?
 
Mottie said:
Out of interest, what’s the difference between setting it on auto compared to setting it on the max KW of the boiler?
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It just states that in Auto the "Product automatically adjusts the max. partial heat load to the current system demand" one might say that it allows the boiler output to operate right up to its max, 30kw in this case, so practically speaking, no different to having it manually set to 30kw?, but I have seen at least one case where setting it to max (from Auto) initially allowed the boiler to reach target temperature but after a few days the same problem occured, "cured" by switching it back again to Auto!!, Vaillant might know.

1704806417723.png
 
Johntheo5 said:
It just states that in Auto the "Product automatically adjusts the max. partial heat load to the current system demand" one might say that it allows the boiler output to operate right up to its max, 30kw in this case, so practically speaking, no different to having it manually set to 30kw?, but I have seen at least one case where setting it to max (from Auto) initially allowed the boiler to reach target temperature but after a few days the same problem occured, "cured" by switching it back again to Auto!!, Vaillant might know.

View attachment 328529
Click to expand...
Maybe auto works best in conjunction with the Vaillant controls?
 
windsortg said:
thanks @DP. What I am finding (and I noticed this, this morning) is that once the room stat setting has been reached, i.e. to 21.5C, the room stat sends a signal to the boiler to turn off. When the room temp drops down to 21C, it sends a demand to the boiler for heat. I noticed the boiler flow temp takes a long time to rise, and it will not go above 58C. The radiators no longer become hot.

Therefore, I am finding that the boiler is not reaching peak fire (i.e. boiler target temp of 65 degrees). d.00 is still set to 'Automatic'
Click to expand...
Proper service is the way forward
Blocked gas line can restrict gas flow hence proper boiler operation
 
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