Hello,

I have a Gas condensing combination boiler.

Make: Vaillant

Model:ecoTEC+ 937

Recently out of interest I decided to see what is the return
temperature when the boiler is doing CH, I found that with a flow
temperature of 60 degrees the return temperature was 54 degrees. Every
time I check there appears to be only a 6 degree differential across
the flow and return, I assume this is not so good and the differential
should be around 11 degrees or 20 degrees.

Is there way to make the differential greater?

Is it do with the radiator sizes?


Thank You.

In article ,
writes:
Hello,

I have a Gas condensing combination boiler.

Make: Vaillant

Model:ecoTEC+ 937

Recently out of interest I decided to see what is the return
temperature when the boiler is doing CH, I found that with a flow
temperature of 60 degrees the return temperature was 54 degrees. Every
time I check there appears to be only a 6 degree differential across
the flow and return, I assume this is not so good and the differential
should be around 11 degrees or 20 degrees.

It doesn't have to be, and at 60C flow, you are most unlikely
to achieve a 20 degree differential.

Does your boiler control the pump speed? In this case it's doing
the right thing, maintaining the return temp below 55C, which is
actually what matters for condensing operation.

Is there way to make the differential greater?

Is it do with the radiator sizes?

Yes, and flow rate.
Were your radiators sized for a condensing boiler (70/50) or
a conventional boiler (more like 81/70)? If they were designed
for 81/70, then at 60 flow I would expect exactly the drop
you're seeing.

So it could be that boiler is modulating burner and pump speed
exactly correctly, and/or that your radiators were designed for
81/70 -- they both give the answer you're seeing.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 16 Nov, 21:50, (Andrew Gabriel) wrote:
In article ,
writes:

Hello,

I have a Gas condensing combination boiler.

Make: Vaillant

Model:ecoTEC+ 937

Recently out of interest I decided to see what is the return
temperature when the boiler is doing CH, I found that with a flow
temperature of 60 degrees the return temperature was 54 degrees. Every
time I check there appears to be only a 6 degree differential across
the flow and return, I assume this is not so good and the differential
should be around 11 degrees or 20 degrees.

It doesn't have to be, and at 60C flow, you are most unlikely
to achieve a 20 degree differential.

Does your boiler control the pump speed? In this case it's doing
the right thing, maintaining the return temp below 55C, which is
actually what matters for condensing operation.

Is there way to make the differential greater?

Is it do with the radiator sizes?

Yes, and flow rate.
Were your radiators sized for a condensing boiler (70/50) or
a conventional boiler (more like 81/70)? If they were designed
for 81/70, then at 60 flow I would expect exactly the drop
you're seeing.

So it could be that boiler is modulating burner and pump speed
exactly correctly, and/or that your radiators were designed for
81/70 -- they both give the answer you're seeing.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Thank you,

I don't know how they were sized, but I forget to add that if the
boiler is running both heating zones the differential is about 12- 15
degrees.
One zone has 10 radiators and the other has only one.
The 6 degree differential was with the 10 radiator zone.