How should I measure delta T at the boiler?

[Orroroo]

How can I see that I am actually benefitting from condensing at the boiler (I've got a relatively cheap measuring unit with two k clamp thermocouples)

As an example measurement I can see 72c on the boiler display but only 63c on the flow pipe just above it and then 56c on the return pipe.

Is the delta T boiler temp vs return or flow pipe vs return?

I'm obviously an amateur and confused.... do I have to do multiple measurements and average? (the unit seems to have a max, min and average function which I haven't explored yet)

Also how long should you leave the clamp on the pipe to get a true reading?

Also it would seem that if I use both thermocouples, one on flow and one on return I get a false reading - with the flow and return pipe temperatures much closer together - I'm guessing that this is the cheapness of the unit (£19)

 

[MNW67]

What boiler make and model? How old?

Some let you read the return on the display menu.

 

[oldbuffer]

1. Provided the return temperature at the boiler is 55 degrees Celsius or lower, the boiler should run in condensing mode. You don't need to know the flow temperature to measure this.
2. What the flow temperature is to get the return to 55 or lower depends on the amount of heat lost from the hot water as it circulates. This in turn depends on the temperature you are trying to achieve, and how quickly you want to achieve it from a cold start.
3. "Delta T" is usually used to express the difference between the average temperature of a radiator (i.e. (flow temp + return temp)/2) and the required temperature of the space it is heating.

 

[Orroroo]

What boiler make and model? How old?

Some let you read the return on the display menu.

Worcester Hi Flow CDi 440 - installed in 2010, can’t spot anything in the manual but don’t want to fiddle with engineering menus particularly

 

[Orroroo]

1. Provided the return temperature at the boiler is 55 degrees Celsius or lower, the boiler should run in condensing mode. You don't need to know the flow temperature to measure this.
2. What the flow temperature is to get the return to 55 or lower depends on the amount of heat lost from the hot water as it circulates. This in turn depends on the temperature you are trying to achieve, and how quickly you want to achieve it from a cold start.
3. "Delta T" is usually used to express the difference between the average temperature of a radiator (i.e. (flow temp + return temp)/2) and the required temperature of the space it is heating.

OK, thanks. I thought delta T was the difference between flow and return

This is the nub I think.

Outside temperature was 5c this morning and it took 4 hours to lift the temperature in the dining room from 17c to 21c.

The dining room rad and upstairs rads are on a 1 pipe system whilst most of downstairs is on 2 pipe so I am guessing this is my fundamental problem - speed in warming the house up

Second problem is using 30000 kWh of gas pa!!

 

[Johntheo5]

How can I see that I am actually benefitting from condensing at the boiler (I've got a relatively cheap measuring unit with two k clamp thermocouples)

As an example measurement I can see 72c on the boiler display but only 63c on the flow pipe just above it and then 56c on the return pipe.

Is the delta T boiler temp vs return or flow pipe vs return?

I'm obviously an amateur and confused.... do I have to do multiple measurements and average? (the unit seems to have a max, min and average function which I haven't explored yet)

Also how long should you leave the clamp on the pipe to get a true reading?

Also it would seem that if I use both thermocouples, one on flow and one on return I get a false reading - with the flow and return pipe temperatures much closer together - I'm guessing that this is the cheapness of the unit (£19)

Flow and return temperatures do generally refer to the boiler, the flow temperature as measured by the clamp on the flow pipe should allways read the same as the boiler displayed flow temperature, the actual boiler return temperature however can read 10C or more higher than the return as measured on the return pipe even if the clamp reading is 100% accurate, this is because a lot (most?) system boilers have internal bypasses that open automatically, Vaillants have the bypasses opening at a default head (dP) of only 2.5M, it can be adjusted but only up to 3.5 or maybe 4M, so you might go to a lot of trouble getting your rad return temperatures down to say 40C to give a very reasonable condensing effect but the by pass might increase this to 50C or higher, don't know your boiler has this internal bypass or not of if you can read the boiler return temperature from the parameters which may be in the menu.

 

[MNW67]

Outside temperature was 5c this morning and it took 4 hours to lift the temperature in the dining room from 17c to 21c.

The dining room rad and upstairs rads are on a 1 pipe system whilst most of downstairs is on 2 pipe so I am guessing this is my fundamental problem - speed in warming the house up

Have you had this problem since 2010 when you got the boiler?

 

[Orroroo]

Flow and return temperatures do generally refer to the boiler, the flow temperature as measured by the clamp on the flow pipe should allways read the same as the boiler displayed flow temperature, the actual boiler return temperature however can read 10C or more higher than the return as measured on the return pipe even if the clamp reading is 100% accurate, this is because a lot (most?) system boilers have internal bypasses that open automatically, Vaillants have the bypasses opening at a default head (dP) of only 2.5M, it can be adjusted but only up to 3.5 or maybe 4M, so you might go to a lot of trouble getting your rad return temperatures down to say 40C to give a very reasonable condensing effect but the by pass might increase this to 50C or higher, don't know your boiler has this internal bypass or not of if you can read the boiler return temperature from the parameters which may be in the menu.

Oh ‘eck…..this is well above me I’m afraid

 

[Harry Bloomfield]

Oh ‘eck…..this is well above me I’m afraid

Digital ones are both quicker to react, more accurate, and easier to interpret. I posted a link a while ago, to a pair I bought, just clip the sensor to the pipe, with a bit of pipe insulation, to promote a quick accurate response. I think I paid less than £5 for the pair of them.

 

[Orroroo]

Have you had this problem since 2010 when you got the boiler?

Possibly - I was working full time up until 2017 when I retired so I was used to a cold house in the morning.
The boiler before the Greenstar was a SIME which didn't condense & I think the plumber who installed it set it to maximum so it was warm by "brute force" & lots of gas.

I got fed up with buying a new PCB every year for the SIME so swopped it out for the Greenstar.

I've started a new conversation about 1 vs 2 pipe but I think i've worked out that its this that is the cause of the problem