Biasi 24s overheat switch tripping

[Agile]

A 24kw boiler in the middle of winter will not produce HW at a temperature that calls for flame modulation. I suggest you try this experiment when cold water is around 6 or 7 degrees C.

Am I to believe you are the only engineer who sets the min max gas rates? If the rate is already correct, why do you need to reset it?

A 24 kW boiler will modulate back when the flow rate is lowered until the boiler can heat the water with less than full power.

I doubt that I am the only engineer who sets min/max gas pressures. But I do see many boilers where the last engineer did not! Many dont seem to even know HOW to set them.

If the heat transfer is poor then the temperature of the primary rises but it still transfers heat.

I dont see this discussion going anywhere.

Tony

 

[DP]

It has been amply clear several replies back, this thread is going nowhere as you have failed to tell me why you think I am wrong.

I am saying a boiler will show a temperature of 70 degrees Centigrade measured at the flow pipe in the boiler, when it is delivering MI designated hot water at the outlet, HW stat at max, gas pressure being as per the MIs. Tony you are invited to say why I will not see said temperature. You are not allowed to vary the settings.

To deviate from above will be taken as argument lost and I will continue to test and set boilers the way I have been doing, instead of adopting your method. So, stay focused and let us bring this thread to an amicable end. Remember I have applied this test to boilers of varied construction, brand new to old clockwork beasts, all working well and fully operational be it with a layer of oxide in the gut or brand spanking new heat exchangers scrubbed with latest magic solutions.

 

[Agile]

I cannot comment on your test as its different to what I do. They are not comparable as they set out to achieve different things.

The temperature recorded on your test will vary according to the water flow rate and inlet temperature.

I set the boiler up as you do but only to measure the max burner pressure. I then reset to how a typical user would be setting it.

I think my way of testing is more helpful to me but obviously you can do whatever you like.

Tony

 

[DP]

The temperature recorded on your test will vary according to the water flow rate and inlet temperature.

Totaly disagree with statement. You fail to see the point I am making. You seem not to be reading what I am posting. Inlet temperature is of no consequence as primary temperature is what is being recorded. Regardless of the inlet temperature, when boiler set as I have indicated will heat the cold water by 35 degrees C for delivery at the tap. Flowrate is constant as indicated in the manual.

It is clear to me that you have failed to demonstrate how you deem my finding to be erroneous as you suggested earlier in the thread. I will welcome future discussioin based on solid foundation instead of constantly shifting goalposts that your replies appear to be based on.

 

[Homesafe]

Newgas, my observation of combi boilers suggests, when incoming water temperature is in single figures, and HW stat at max with hot tap at full flow, burner does not modulate as it is working flat out. and so primary temp. is 70 deg.C
Have seen this time and again. Even had calls from customers compalining hot water is not hot enough. 5 degrees C of cold water will be 40 degrees at hot tap. Ease back on the hot tap will push up the temperature and modulation comes into the picture

very clearly explained DP, thanks.

i have read all above post and the from what i have learnt your method is correct.

i don't understand Mr. T's methodology

 

[Agile]

I do fail to see why you think the boiler flow temperature will be fixed at 70° C regardless of the mains water temperature.

But Newgas thinks he understands so perhaps he should explain to us?

Tony

 

[Homesafe]

I do fail to see why you think the boiler flow temperature will be fixed at 70° C regardless of the mains water temperature.

But Newgas thinks he understands so perhaps he should explain to us?Tony

trying to be cunning won't get you out of this one hony,

and you also should explain your lack of response to your OWN question's to me.

or is it too much for you

 

[Agile]

I do have jobs to do and a life away from forums!

 

[DP]

I am not dreaming, thinking or making things up- it is a case of seeing with my own eyes results on a multimeter connected to a termistor probe with settings I have been writing about over the last four pages.

Searching minds like Newgas, will at least carry out checks as I have detailed, and then make up their own mind whether I am right or wrong.

Sad that someone like yourself, a clever person I must admit, should take a blinkered approach and fail to admit that for once someone else just could be right and you for a change be on the receiving end of a bit of knowledge.

This said, I have made my point as I have seen nothing that prompts me change my procedure during setting up a combination boiler. This does not mean my head is in the sand and I will not look at, evaluate and adopt a method that makes me a better heating engineer.

 

[Agile]

I cannot say that you are right or wrong!

But what you do is not the same as what I do and I think my method checks more that yours.

As far as I can gather, your method would not identify a lack of downwards modulation. Nor a gas valve with a min too high.

My method, I think checks all these aspects very quickly. To recap:-

Max temp and max water flow then check MAX burner pressure [ reset if necessary ]

Dis mod coil lead to check MIN burner pressure [ reset if necessary ]

Reduce flow rate to about what the boiler can raise to about 43°. View system flow temp on boiler gauge/display. Then turn back the temp control knob slowly and check that it modulates down.
Using that setting most boilers will be flat out and will not modulate down until the knob is about 1/3 down which would often be the normal setting as it would be the setting to deliver 43°.

I use 43° because thats a temperature I can judge easily with my hand as well as being a typical users setting.

I am not suggesting that my method is best, correct or anything else but I do think that it best tests all operations of the boiler very quickly and easily. At our fixed charges I cannot spend 30 minutes on a lab standard performance test. I aim to find and fix the fault and be paid within 75 minutes, ideally 60 minutes. Client usually wants 10-15 minutes to discuss boiler and charges and slowly find his payment. All I set out to do is quickly assertain the boiler is functioning as expected. Probably 70% of the boilers I see have a partially blocked plate.

If anyone else chooses to use different methods that their perogative!

Tony

 

[DP]

I cannot say that you are right or wrong!

I have to disagree with DP here.

Perhaps he does not visit many of these boilers?

I wonder what iyou idea of right and wrong is.

As far as I can gather, your method would not identify a lack of downwards modulation. Nor a gas valve with a min too high.

Presuming a lot are you not Tony? What makes you think the gas rates have not already be checked and verified along with correct operation of modulation?

Using that setting most boilers will be flat out and will not modulate down until the knob is about 1/3 down which would often be the normal setting as it would be the setting to deliver 43°.

Totaly unbelievable. I wonder if you have tried running the boiler at max during HW AND noted lack of modulation or is it pure conjecture. I wonder if Newgas, might want to carry out this experiment and post his finding. After all it would be an exercise that would give him better understanding of boiler operation and modulation. I further note that your preferred and 'typical' setting is 33% down on max and preferred temperature of water at tap as judged by the back of your hand, is 43 degrees.

Pray tell how you aim to achieve this temperature when cold water is at 5 degrees C and stat is 33% down on max?

I am not suggesting that my method is best, correct or anything else but I do think that it best tests all operations of the boiler very quickly and easily. At our fixed charges I cannot spend 30 minutes on a lab standard performance test. I aim to find and fix the fault and be paid within 75 minutes, ideally 60 minutes. Client usually wants 10-15 minutes to discuss boiler and charges and slowly find his payment. All I set out to do is quickly assertain the boiler is functioning as expected. Probably 70% of the boilers I see have a partially blocked plate.

Fail to see what above has to do with 70 degrees C displayed on temperature gauge with HW stat setting at max with designated flow rate at hot tap. I see it as evasive tactics.

 

[Agile]

Pray tell how you aim to achieve this temperature when cold water is at 5 degrees C and stat is 33% down on max?

As I said, I set the water flow rate so that about 43° is achieved with the temperature knob on the appropriate setting to achieve this temperature. I then reduce the flow rate further to ensure the boiler modulates down and maintains that output temperature.

Tony

 

[DP]

I suspect you do not see the point I am making. A combi will raise the cold water temperature by 35 degrees C. With incoming cold at 5 degrees C, HW stat at max, flow rate as specified, delivery temperature will be 40.

Can you explain how 43 degree hot water will be delivered by REDUCING the HW stat setting by 33%? At full wack, combi will struggle to deliver 40. My dim brain is blowing a gasket wondering how you can achieve your desired settings.

 

[Agile]

A 24 kW has the power to raise about 9 li/min by 35° C.

It has the power to raise about 6 li/min by 52° C

Thats providing the temperature control does not modulate it back.

Most boilers have a hot water control which allows setting between about 35° C and 55° C.

While testing I reduce the flow rate to about 7-8 li/min to the point that the boiler on max gives about 43° C.

I turn the control knob down to ensure it modulates downwards fully.

If, as usual, I want to check the heat transfer of the secondary HE, I run it for a minute at the 7-8 li/min and 43° to see what secondary temperature is reached. Thats the test where I dont expect to see more than about 60-65° C

I then turn the DHW temp control down to the point where its just about to modulate down and then reduce the flow rate further to check the boiler is controlling the temperature at about 43° C.

I also turn the control knob slowly down to ensure it modulates downwards fully.

I do these tests to ensure that when I leave it its working correctly in the way that most users would have it set and there are no other faults apparent OR that I am aware of any slight deficiencies. Depending on the user, I sometimes restrict the flow rate at the boiler to be closer to what the boiler can heat.

Doing all this only takes about one or two minutes and will show up a dirty or damaged HW control pot for example.

Tony

 

[DP]

If, as usual, I want to check the heat transfer of the secondary HE, I run it for a minute at the 7-8 li/min and 43° to see what secondary temperature is reached. Thats the test where I dont expect to see more than about 60-65° C

???? What are you on about.

What you have posted above every heating engineer length and breadth of Britain does without making a song and dance about.

What I find quite strange is that a 24kw combi with miniscule flowrate of hot water being throttled to 7- 8l per minute.

The reply has absolutely nothing to do with my query. With over a thousand views and me asking a specific question to which no answer has yet been delivered other than plenty of smoke screen.