Boiler flow and return temperatures.

[Harry Bloomfield]

If you’re going to be pedantic Harry then it’ll be attached to the boiler flow, rather than in it. I didn’t say the sensor would be inside the heat exchanger. The temperature relates to the circulated water. I know exactly where the sensors are on a Vaillant EcoTEC.

I'm sure you do, but your suggestion that it was measuring the heat-exchanger temperature was obviously wrong, and possibly a source of confusion for the OP.

 

[Harry Bloomfield]

I suppose I could do but would that be more economical - heating rooms we are not in? During the day, both kitchen/diner rads are on from 6.00am until approx 7.00p.m. so I imagine the return temperature is in between the other two. Only have the four rads on from approx 7.00 - 10.30pm.

Your problem appears to be one of needing two separate flow temperatures, for best economy. One for CH, another for HW production. The fancy Vaillant control system can do that, but it can only supply one at one time, so your heating goes off, when ever there is a call to heat the cylinder. In practice, that is not an issue, unless your house is starting up from cold.

 

[Mottie]

It would be well worth you're installing the Vaillant control system, for your boiler, it does work rather well.

Would that override/interfere with my hive control setup? I had to have the 24v link removed to use non-Vaillant controls as the Vaillant controls are 24v and that’s how they come set up. Can’t see how you would run a low voltage and mains voltage controls at the same time.

If it’s just for a different hot water flow temp, I doubt I’d see much benefit - in the summer when the heating is off, my gas usage for hot water and cooking is only about 35p a day.

 

[Harry Bloomfield]

Would that override/interfere with my hive control setup? I had to have the 24v link removed to use non-Vaillant controls as the Vaillant controls are 24v and that’s how they come set up. Can’t see how you would run a low voltage and mains voltage controls at the same time.

It would - it would need to completely replace the Hive, I think. The Vaillant is a bus system, partially wireless depending on version.

Mine uses a wireless stat + control panel/display, wireless outdoor temperature sensor, bus to unit near cylinder.

 

[Mr Chibs]

Not trying to hijack this thread, but I bought some aquarium thermometers (thanks Harry) to measure the flow and return.

My heating output is set to 45°.
Flow @ 45°
Return @ 34°

Does this mean my boiler will always condense, as heating output is only set to 45°? or is it not that straight-forward?

 

[Harry Bloomfield]

Does this mean my boiler will always condense, as heating output is only set to 45°? or is it not that straight-forward?

45C is well into the condensing flow temperature. Providing it stays that low, it will be very efficient.

 

[hllns]

My heating output is set to 45°.
Flow @ 45°
Return @ 34°

Does this mean my boiler will always condense, as heating output is only set to 45°? or is it not that straight-forward?

The return is the important value in relation to condensing efficiency, 34 degrees would not only means it's condensing but that efficiency is around 95%!

 

[Mr Chibs]

Thanks for this, have an Intergas boiler.

Thought I would try running it 24/7 at these temps, on the whole it's comfortable.

Also have a wood burner in the lounge (which is the coldest room) for evenings, thermostat is not in the lounge.

Took a while to get warm, as the radiators hardly feel that warm, but so far, I don't think I will set a programme again, doesn't seem worth the hassle, not sure when I'll turn it off.

 

[Harry Bloomfield]

Took a while to get warm, as the radiators hardly feel that warm, but so far, I don't think I will set a programme again, doesn't seem worth the hassle, not sure when I'll turn it off.

My system has the advantage of being able to automatically decide just how hot it needs to set the flow, to hit it's set room temperature within a reasonable time frame.

 

[Mr Chibs]

Is this boiler specific or something to do with Opentherm?

 

[Harry Bloomfield]

Is this boiler specific or something to do with Opentherm?

It is a Vaillant boiler, with the full Vaillant control system. It's not Opentherm, it's Vaillant's own bus system.

 

[Mottie]

My system has the advantage of being able to automatically decide just how hot it needs to set the flow, to hit it's set room temperature within a reasonable time frame.

I have a Vaillant boiler and Hive controls. I can choose wether to set the boiler to come on at a set time or to be at a certain temperature at a set time. If I choose the latter, the boiler decides what time to come on.

 

[Harry Bloomfield]

I have a Vaillant boiler and Hive controls. I can choose wether to set the boiler to come on at a set time or to be at a certain temperature at a set time. If I choose the latter, the boiler decides what time to come on.

Which I think misses out the bit where the controls can directly inform the boiler, just how much to modulate.

 

[Mottie]

Which I think misses out the bit where the controls can directly inform the boiler, just how much to modulate.

It modulates on its own - I can see and hear it.

 

[Harry Bloomfield]

It modulates on its own - I can see and hear it.

Yes, but it can only modulate, based on it's own flow temperature.

Mine modulates based on it's flow temperature, plus on room temperature - it knows the desired room temperature, knows the current temperature, knows the outdoor temperature, so from that can precisely match it's modulation to the need for heat output.