Pump head settings - which is best?

[berty3000]

Hello,

I have a Worcester Greenstar 25i, combi boiler. House is a detached bungalow with 9 radiators. These include a towel rail, a small ensuite radiator, a smallish kitche one, two vertical radiators for living areas, and then a mix of medium sized horizontal ones, all new. They all have TVRs fitted apart from one of the verticals, which is located where the thermostat is, and the towel rail. Some of the pipework is 10mm but there is a reasonable amount that is the original 22mm and 15mm. The pipework all runs up walls and through the attic.

I find that the difference between flow and return temperature is only about 5C running at 52C flow.

My boiler pump head setting is 4 (constant high). Does my system need to have such a high pump setting? If not, what is recommended instead? I see there is a variable speed option as well. See image. Would there be any risk of damage by trying out medium instead?

Any advice welcome.
Thanks

 

[denso13]

Would there be any risk of damage by trying out medium instead?

No, turn it down and check if everything still heats up ok.

 

[berty3000]

No, turn it down and check if everything still heats up ok.

Thanks!

How about variable speed?

 

[berty3000]

It heated the house as quickly as usual and very well on setting 2 (low to medium)... so I'm tempted to put it to the lowest. Is there any downside to having it low other than the issue of it not heating the house as well or quickly? Or is it a case of, the lower the better?

 

[Harry Bloomfield]

It heated the house as quickly as usual and very well on setting 2 (low to medium)... so I'm tempted to put it to the lowest. Is there any downside to having it low other than the issue of it not heating the house as well or quickly? Or is it a case of, the lower the better?

The lower, the better, consistent with it providing enough heat to the house, and to warm it from cold in a reasonable time.

 

[BlueLoo]

Depends.

 

[berty3000]

The lower, the better, consistent with it providing enough heat to the house, and to warm it from cold in a reasonable time.

Thanks. Do you know what the variable speed thing is all about and if that's a good option?

 

[Mottie]

It heated the house as quickly as usual and very well on setting 2 (low to medium)... so I'm tempted to put it to the lowest. Is there any downside to having it low other than the issue of it not heating the house as well or quickly? Or is it a case of, the lower the better?

I assume that the slower the circulation, the more chance of getting heat out of the radiator giving you a cooler return. Only downside is that it may take longer to warm up from cold. Have it on as low as possible setting and see how it goes.

Do you know what the variable speed thing is all about and if that's a good option?

I asked that before and I was told the variable speed is not good if you have a modulating boiler.

 

[BlueLoo]

Thanks. Do you know what the variable speed thing is all about and if that's a good option?

I had written a reply but didn't see that you've a combi, not the system boiler I'd assumed.

You would think Auto is a PP mode. (Proportional pressure)
However, the iom pump curve seems to show a std constant speed pump curve for mode 0 which is a bit odd unless I'm missing something.


The pump is factory set normally in CP mode 4 (Constant pressure).

As per above, go as low as the system will tolerate

 

[berty3000]

Thanks for all the responses, much appreciated.

Only thing I'm noticing now is that, despite the flow temperature being set to 52C, and the water being set to 45C, that the temperature gauge is saying 58C. The heating turned off several hours ago. I did do the dishes about 20 mins ago using hot water but that temperature would be well below 58C. Normal?

 

[berty3000]

Hasn't occurred to me before as this boiler was here when I moved in, but isn't the 24i oversized for my home?

In which case, what else can I do to reduce its potency?

 

[desktop987456]

Theoretically speaking and what I have read in books, I think you need to know:
- the head loss of your system (depends on pipe size, flow rates, design and layout of rads) so you can draw system curve of your heating system.
- pump curves of your model from manufacturer which will tell you differential pressure that each settings will produce.
- the point where the two curves intersect (system and pump curve) is the point where you should be setting pump speed (without knowing headloss you are just gessing).

see attached for different layout and configurations for heating system. I have also attached a pump curve schematic of commonly used pump 15-50 in most heating systems.
HTH

 

[berty3000]

Ok, so the lowest pump head setting works fine.

Now I am interested to explore other options in the settings:

2.1A (Max CH power [LowNox below 13KW] )

Current setting: 24KW. Is there merit in turning this down?

2.1B (Max DHW power)

Current setting: 25KW. Same question.

2.2C (air purge mode)

Current setting: Off

2.3B (anti fast cycle time)

Current setting: 5 mins.

2.3C (anti fast cycle flow temp)

Current setting: -6

2.9E (flow turbine signal delay)

Current setting: 2.

Thoughts on best settings, especially for efficiency and cost effectiveness?