Boiler Short Cycling

[bagaceratops]

Just now, if (when) running continuously, note those pump values and also d.40 & d.41 and we can compare them.
Preferably with rads only on.

Thanks will have a look and post.
As well as the 8 rads I have 3 large towel rails that run off the radiator circuit too.
When I say large that are each about 6ft tall.

 

[bagaceratops]

Just now, if (when) running continuously, note those pump values and also d.40 & d.41 and we can compare them.
Preferably with rads only on.

Hi,

Boiler is modulating fine at present.
Just rads calling for heat (and maybe DHW), but UFH off

Flow is 70 degrees, return is 49
Pump is reading - 8.2 Watts, 1.2 metres head and 0.8 m3/hr
I checked d0 and it is set to 30

Thanks

Andrew

 

[John.g]

Thats a amazingly low head, anyway, by calculation, using the pump flow of 0.8m3/hr and the boiler dT of 21C gives a boiler output of 19.53kw, the 8 rads at rated output = 9.4kw but because of the flow/return temps will be outputing ~ 74% of their rated output, say 7kw. So 12.53kw going elsewhere??.
If the pump values are still similar suggest reducing d.0 to 15kw, if the above boiler output is valid then the flow/return temps should reflect a 15kw boiler output and would confirm that d.40 & d.41 are reading accurately.

 

[John.g]

Does your system have a low loss header or close coupled Tees as the very low head seems to indicate this and the pump is on the lowest PP setting A, I can't see any PP or CP settings, apart from A,B or C for this pump (for interest), do you have any values/ranges for them?.

 

[bagaceratops]

Does your system have a low loss header or close coupled Tees as the very low head seems to indicate this and the pump is on the lowest PP setting A, I can't see any PP or CP settings, apart from A,B or C for this pump (for interest), do you have any values/ranges for them?.

Dont believe there is a low loss header and no close coupled tees. Just a standard bypass valve

Re the pump again not really sure which setting it should be on, assume PP as I have rads with thermostatic valves, but pump also has the eAdapt setting, constant pressure and also fixed speeds

If I run the pump on curve B or C then the head and flow increases.
I found this for the specs on the pump

https://www.pumpsukltd.com/pub/media/bss/productattachment/191027281_c_w06-2020_ecocirc-50hz_en.pdf

 

[John.g]

The pump curves are in your attachment, I reckon that you would get ~ 1.1m3/hr @ 2.1m on PP B and ~ 1.4m3/hr @ 3.6M on PP C.

This doesn't solve your problem however, theoretically PP C should reduce the dT from 14C to 8C and allow the boiler to get closer to its SP temperature before recycling and might reduce the 20C dT to 11.5C even though no problems with the boiler once it reaches its SP.

Have you reduced d.0??.

 

[bagaceratops]

Thats a amazingly low head, anyway, by calculation, using the pump flow of 0.8m3/hr and the boiler dT of 21C gives a boiler output of 19.53kw, the 8 rads at rated output = 9.4kw but because of the flow/return temps will be outputing ~ 74% of their rated output, say 7kw. So 12.53kw going elsewhere??.
If the pump values are still similar suggest reducing d.0 to 15kw, if the above boiler output is valid then the flow/return temps should reflect a 15kw boiler output and would confirm that d.40 & d.41 are reading accurately.

Interesting,

I dropped D0 to 15 and set the pump to PPB and it stopped cutting out. But it did not appear enough to heat the water. I had rads on and one UFH circuit at the time.
Then all circuits started calling for heat so increased d0 to 25, It started its cutting out. Gradually reduced D0 to 21 where it appears not to cut out, this is with most of the circuits on, but it is taking much longer to heat up, although not cycling.

Pump is showing circa 3.5 metres head and 1.5 m3 flow this is on curve B

Should I be using curve C?
Not having any heat loss calculations for my house again dfifficult to know what boiler should be on.

This is really interesting stuff, my plumber / heat engineer never discussed any of this.

Thanks

 

[ShaunCorbs]

Easy enough to do go round and calculate the size of your rads and find similar ones on the internet there output will be listed so Calc all the rads and total it up

Then give us the flow rate of each ufh loop via the flow meter and we can work out the rough load ufh wise

 

[John.g]

Interesting,

I dropped D0 to 15 and set the pump to PPB and it stopped cutting out. But it did not appear enough to heat the water. I had rads on and one UFH circuit at the time.
Then all circuits started calling for heat so increased d0 to 25, It started its cutting out. Gradually reduced D0 to 21 where it appears not to cut out, this is with most of the circuits on, but it is taking much longer to heat up, although not cycling.

Pump is showing circa 3.5 metres head and 1.5 m3 flow this is on curve B

Should I be using curve C?
Not having any heat loss calculations for my house again dfifficult to know what boiler should be on.

This is really interesting stuff, my plumber / heat engineer never discussed any of this.

Thanks

Does the cycling still only occur when the dT reaches 14C?.

You can calculate the boiler output at any given time by
(m3/hr16.67x60xdT/860)kw, At 14C dT, boiler output is (1.5x16.67x60x14/860), 24.4kw. So if rads only on easy to calculate their combined output once you also note the boiler flow/return temperatures.

A flowrate of 1.5m3/hr, 1500LPH should result in a Hx dP of 3.6m, 2.38x(1500/1220)^2, but your pump is only developing 3.5m so something not adding up?, boiler internal or external bypass passing, or another pump hidden away some where?.
Even If the boiler has a internal bypass thats faulty presume the boiler will still measure the flow/return temps correctly.
The pump, judging by your original pump values for PP A seems correct, can you just post the power W + flow & head while running in PP B and we can soon tell if these values add up.

 

[bagaceratops]

Does the cycling still only occur when the dT reaches 14C?.

You can calculate the boiler output at any given time by
(m3/hr16.67x60xdT/860)kw, At 14C dT, boiler output is (1.5x16.67x60x14/860), 24.4kw. So if rads only on easy to calculate their combined output once you also note the boiler flow/return temperatures.

A flowrate of 1.5m3/hr, 1500LPH should result in a Hx dP of 3.6m, 2.38x(1500/1220)^2, but your pump is only developing 3.5m so something not adding up?, boiler internal or external bypass passing, or another pump hidden away some where?.
Even If the boiler has a internal bypass thats faulty presume the boiler will still measure the flow/return temps correctly.
The pump, judging by your original pump values for PP A seems correct, can you just post the power W + flow & head while running in PP B and we can soon tell if these values add up.

View attachment 80657

Hi,

So boiler settled down and is modulating ok now
flow = 70, return = 58
Pump is running at 26 Watts, 3.7 metres head and 1.42 litres per second
I have rads on, DHW is on, but not sure if calling for heat
Two UFH zones are on (on seperate manifolds)
UFH 1 is about 50 metres and 2 litres per min
UFH2 is 3 loops of 80,80 and 50 each running at 2 litres per min

There are 3 pumps on my system
Main circulator plus each UFH manifold has its own pump