Boiler central heating return temperature?

330d

I have balanced my central heating system in my house. All the heaters are showing a temperature at the top between 55-60c.

And at the bottom they are 10-12c temperature drop. Reading online this is what is recommended.

My boiler outlet temperature is currently set to 70c. I know this is higher than what is recommended and not very efficient but I noticed the heaters do heat up much quicker Vs 60c setting.

But what I'm confused about is it's showing a return flow temperature of 67c. I was expecting the return temperature to be much lower than that. Surely the water is not loosing 3c heat after heating my radiators?

Do I need to somehow lower the return temp?

Thanks 

sheenas

The idea is that the boiler runs for longer at a lower temperature. This does mean it takes a bit longer to heat up but runs more efficiently. The boiler will what’s Called modulate. The limiting factor is radiator size , small radiators not being able to heat a room, if you turn the flow temperature down to much. I run mine at 55c you could try lower if you like, but I would keep it above 50c Thu. 

QrizB

330d said:

I have balanced my central heating system in my house. All the heaters are showing a temperature at the top between 55-60c.

And at the bottom they are 10-12c temperature drop. Reading online this is what is recommended.

So the return temp from the bottom of your radiators is around 45C?

330d said:

My boiler outlet temperature is currently set to 70c.

If your flow temp is 70C, why is the top of your radiator only 60C?

330d said:

But what I'm confused about is it's showing a return flow temperature of 67c.

If the bottom of your rads is at 45C, why is it now 67C when it gets back to your boiler?
Is your bypass valve passing when it shouldn't?

330d

QrizB said:

330d said:

I have balanced my central heating system in my house. All the heaters are showing a temperature at the top between 55-60c.

And at the bottom they are 10-12c temperature drop. Reading online this is what is recommended.

So the return temp from the bottom of your radiators is around 45C?

Yes correct 

330d said:

My boiler outlet temperature is currently set to 70c.

If your flow temp is 70C, why is the top of your radiator only 60C?

I presume that's because of losses? Or should the top of all radiators be 70C?

330d said:

But what I'm confused about is it's showing a return flow temperature of 67c.

If the bottom of your rads is at 45C, why is it now 67C when it gets back to your boiler?
Is your bypass valve passing when it shouldn't?

Well that's question I'm asking. The boiler is showing a return temp of 67C

QrizB

When you say "the boiler is showing", have you measured the temperatures with the same device that you used to measure the radiators? Or ar you trusting the display on your boler controls?

Is this a combi boiler or do you have a hot water tank? Is the tank also calling for heat?

330d

QrizB said:

When you say "the boiler is showing", have you measured the temperatures with the same device that you used to measure the radiators? Or ar you trusting the display on your boler controls?

Is this a combi boiler or do you have a hot water tank? Is the tank also calling for heat?

It's a system boiler with a tank. Tank is not set to heat when I took these measurements.

And yes I'm using the boiler screen but will use my laser temp gun on the flow and return pipes of the boiler.

Albermarle

330d said:

QrizB said:

When you say "the boiler is showing", have you measured the temperatures with the same device that you used to measure the radiators? Or ar you trusting the display on your boler controls?

Is this a combi boiler or do you have a hot water tank? Is the tank also calling for heat?

It's a system boiler with a tank. Tank is not set to heat when I took these measurements.

And yes I'm using the boiler screen but will use my laser temp gun on the flow and return pipes of the boiler.

A very basic test is to feel the flow and return pipes with your hands. Normally if there was only a 3 degrees drop, you would not be able to detect that, especially as at 70 degrees( ish) , you would not be able to tolerate touching them for more than a few seconds. However if there is a more usual drop of 15/20 degrees, it should be quite noticeable.

Heedtheadvice

Just some quick thoughts ( similar to QrizB bypass Q).

I would expect the rads( top) to be a little below boiler out temp, as you mentioned, losses which will include those from the radiator. 10+degrees seems quite a bit though. I wonder if they have a lot of restrictions of flow with lockshield valve restrictions? That could increase temp loss due to cooling of the rad and maybe letting more hot water bypass the rads perhaps exacerbated by a pump high flow setting such that most of the return water gets very little temp loss?

would still expect it to loose a fair bit compared to boiler output temp and the more the better for efficiency if being lost via rads. Suspect a measurement issue too ( or flow going through boiler wrong way ? 😀 )

Section62

330d said:

QrizB said:

When you say "the boiler is showing", have you measured the temperatures with the same device that you used to measure the radiators? Or ar you trusting the display on your boler controls?

Is this a combi boiler or do you have a hot water tank? Is the tank also calling for heat?

It's a system boiler with a tank. Tank is not set to heat when I took these measurements.

And yes I'm using the boiler screen but will use my laser temp gun on the flow and return pipes of the boiler.

Have you checked the valve controlling the flow to the cylinder is working correctly - they can fail in a position which allows constant flow through the hot water cylinder.  This could explain why the return flow is so hot and the radiators take a long time to heat up... but typically you would know something is wrong because the hot water gets very hot (as hot as the system flow temperature if the boiler runs long enough).

Also, do you have any towel rails/radiators which act as a bypass?  I.e. tee'd off between the pump and the control valve(s).

tacpot12

I suspect it's a measurement issue. IR Thermometers have trouble reading from shiny surfaces, like copper pipes. They read accurately from painted susrfaces, like radiators. I use one of these to measure the flow and return at the boiler: https://www.ebay.co.uk/itm/317034358079

However, the difference that you are seeing is unlikely to all be down to the IR Thermometer struggling to read the pipe temperature correctly (The Flow pipe reading would be off if the Return reading was off, unless one pipe is painted and the other isn't.) I think that culprit is likely to be the automatic bypass valve (ABV) as suggested by QrizB. 

My boiler (Intergas HRE OV 24kW) shows the flow temperature is 72C, but it has weather-compensation, so this is actually the hottest flow temperature and is only used when the outside temperature is -5C or lower. My flow was around 59C and return was 48C (DT = 11) a couple of days ago when the outside temperature was +2C. (Our house is a big, old Victorian terraced house with poor insulation - a project for later this year/early next year). 

You want your return temperature at the  boiler to be 54C or lower to get the benefits of a condensing boiler - assuming you have a condensing boiler. This is why the advice is not to set your flow temperature too high. Try lowering it on warmer days so that the return is less than 54C or fit weather-compensation, or even better, fit a thermostat in the house that has load-compensation.
  

ComicGeek

330d said:

I have balanced my central heating system in my house. All the heaters are showing a temperature at the top between 55-60c.

And at the bottom they are 10-12c temperature drop. Reading online this is what is recommended.

My boiler outlet temperature is currently set to 70c. I know this is higher than what is recommended and not very efficient but I noticed the heaters do heat up much quicker Vs 60c setting.

But what I'm confused about is it's showing a return flow temperature of 67c. I was expecting the return temperature to be much lower than that. Surely the water is not loosing 3c heat after heating my radiators?

Do I need to somehow lower the return temp?

Thanks 

Do you have TRVs installed on the rads? Have you been balancing the rads against a partially closed TRV? That could explain the temperatures as it limits the flow rate into the rad - would then also have a high return flow temp.

Would normally fully open TRVs or remove the sensor head for balancing.