If display is 55 degrees on vaillant boiler is that when boiler is at most efficient?

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I got a eco tec 627 system boiler.

The display is showing about 39 degrees. If it’s at 55 degrees is that when heating is tuning at most eco friendly?
 
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Its the boiler return temperature that determines the boiler efficiency, most boilers just control the flow temperature and the return temperature will obviously be lower than this, by 10C to 20C, so if your flow temp is actually 55C then the boiler will be pretty efficient as the return temp will be 45C to 35C. Outside temperature compensation will reduce the flow temperature automatically leading to greater efficiencies. You can also run a Vaillant in return temperature control but I see very little examples of this on any heating sites.
 

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The TRVs must be open fully for that very low dT. If only a few rads on, in say a (zoned) circuit and your circ pump is set to a very high head then you will get a low dT, rads are supposed to be balanced by throttling the lock shield valves although mine are not and when the (10) TRVs start throttling in, the the return can be as low as 40/45C with a fixed flow temperature of 70C, dT of 30ish.
 
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Thanks. While I’m here. I got a greeniq system boiler with vsmart. I presume the range can be set to auto… and there’s probably little else I need to touch? It’s a 27kw system boiler with 10 to 1 modulation
 
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Its the boiler return temperature that determines the boiler efficiency, most boilers just control the flow temperature and the return temperature will obviously be lower than this, by 10C to 20C, so if your flow temp is actually 55C then the boiler will be pretty efficient as the return temp will be 45C to 35C. Outside temperature compensation will reduce the flow temperature automatically leading to greater efficiencies. You can also run a Vaillant in return temperature control but I see very little examples of this on any heating sites.

The first and last sentences are very interesting. The first because although you're obviously right, I personally look at the flow temperature being important as that shows how much of the exchanger is likely to be below the products of combustions dew point (ie a return at 55 may be 60 within a very short distance of it's entry. A flow at 55 means most of the exchanger may be below a dew point. The lower the flow temp the greater the area of the exchanger for condensing. Just looking at things in reverse.

Also of course how good the exchanger is and the closeness of the flue to return temperatures.

I've not heard of return temp control before, which boiler offers this please?
 
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What’s implications of pump speed being too high? I have 3 floors. It’s a self modulating boiler grreeniq 627.
 
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ΔT (temperature difference across flow and return) is too close. Ideal is 20°C on a condensing boiler.

Too much boiler power, the property can’t absorb it so flow temperature isn’t reduced sufficiently as the water is distributed around the system. Boiler cycles, ΔT closes.

Pump setting too high, even if output matches property load, the water flow is too fast, same result, a close ΔT.

The flow can be restricted to a limited extent at the radiator valves but there is a limit and the system changes all the time as weather and heat loss changes.

There are flow balancing valves available but a bit more expensive.

There are ΔT boilers that one can set a design ΔT on and the pump will target it.

Building height is irrelevant.
 
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IMO too many variables to adjust and decide if a boiler is condensing, not many people wil bother with that, flow temps, weather compensation, trv setting and now pump speed? Presumbly self modulating boiler will modulate down when heat has been acheived. The flow temp is not set correctly by the inmstaller, its left higher most of teh time to suite client as it provides heat.
 
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Would agree, I would venture that most HE boilers are never in condensing mode but they still have a substantial efficiency gain in that a SE Boiler like my 17 year old Firebird with a flue gas temperature of ~ 230C vs a very easily achievable flue gas temperature of say 80C in a HE boiler with a efficiency gain of around 6/7%. However I have no intention of getting rid of my SE boiler as its outstandingly reliable, it's Riello G5X burner has never ever tripped on combustion failure, remarkable IMO since all oil fired boilers spend their entire working lives in cycling mode.
 
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I've not heard of return temp control before, which boiler offers this please?
The Vaillant Ecotech 418, for one, I asked someone in, I think, another heating forum to c/o to return temperature control, here is a extract of my comments on that.

(Vaillant Ecotec 418) briefly c/o to Return Temp control, it had been set to Flow control with a SP of 70C which gave a return temp of 55C, the target temp was then set to 55C on c/o and the flow/return temps then fell to 47C/37C, with a observed d.05 of 36C which is the "Determined heating flow set target temperature", presumably, this was now the calculated return temperature required?. Unfortunately, as there were more pressing problems at the time, the test was not continued, maybe there's a volunteer or two out there?.
 
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(Vaillant Ecotec 418) briefly c/o to Return Temp control, it had been set to Flow control with a SP of 70C which gave a return temp of 55C, the target temp was then set to 55C on c/o and the flow/return temps then fell to 47C/37C, with a observed d.05 of 36C which is the "Determined heating flow set target temperature", presumably, this was now the calculated return temperature required?. Unfortunately, as there were more pressing problems at the time, the test was not continued, maybe there's a volunteer or two out there?.

Are we talking here about the boiler itself monitoring and controlling the return temperature, or a front panel settable control for return temperature? If the latter, then I have not found one.
 

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