Biasi 24s overheat switch tripping

[DP]

They use a stainless plate heat exchanger which have a good thermal transfer and are used in current combi boilers.

They cannot be compared with the older designs using a copper coil in a steel pot which have lower heat transfer and need a higher temperature differential.

I beg to differ. Flowmatic and Excel have the same main heat exchanger. Excel unlike the Flowmatic does not have coil in a pot but a plate to plate HW heat exchanger. Temperature display remains the same for both boilers during hot water demand. Same on Biasi 24S

It would also match mine as well although I dont take much interest in the exact measurements on older design boilers because its not very important for me and many are quite sludged up by now.

Boiler repair, be it an old or a new appliance is indeed based on precise measurements and checks. I fail to see how a heating engineer could give his 100 percent if his attention to details diminished with age of boiler. If that were the case, heaven help the customers with Vaillant Sine or VCWs. Also are you suggesting 24S is not an old boiler?

To suggest every old boiler would be sludged up is same as an earlier statement you made elsewhere where you suggested a 3 bedroom 7 rad property would have the same heat requirement as a bungalow with 16 radiators.

I do not mean to be judgemental or argumentative, more a case of quest for greater knowledge. Looking for facts that will further sharpen my boiler repairing skills.

I go to about 10 per month to repair them and feel that I am very conversant with their operating parameters.

I am not doubting you expertise

 

[DP]

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.

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

 

[Homesafe]

I have to disagree with DP here.

Perhaps he does not visit many of these boilers?

In any case no boiler than I can think of would have a primary temperature of as high as 70°C during normal DHW delivery.
Tony

so what does this mean , agil is well out or he has made a statement
that he can't retract.

 

[DP]

It is nothing to do with scoring points, more a case of sticking to facts.

I have read nothing so far that tells me I am making a mistake.

 

[Agile]

The problem is that unless the boiler is very newly fitted to a clean system then the conditions will not be comparable with a clean plate.

If the plate is clean then there will usually only be about 15-20° differential between boiler flow and DHW temp.

I was refering to "normal" operating conditions! DP mentioned winding DHW temp control to maximum. I was refering to the "usual" operating conditions for that boiler model.

Tony

 

[Homesafe]

Temperature gauge showing 70 during hot water delivery would suggest boiler is functioning correctly while hot tap is running. It would also suggest main heat exchanger and HWHE are both in reasonable condition if hot water delivery and gas rate is correct

have i missed something here as i have not seen OP mention anything about the gas rate or DHW delivery temp.?

it would be good to get a conclusive or common answer considering the "knowlegde" you guy's have

 

[DP]

Tony each post you write says different things. Each reply is with ‘shifted goal post’ to give weight to your reply. You are either not reading what I am posting or choosing to ignore my replies

The debate started with OP saying the gauge on his Biasi 24S indicated 70 degrees during hot water delivery which my experience tells me boiler is working correctly.

On page two very early in the debate I said “ 20/ 80 was set up for flow rate of 9.5l of water at hot tap, burner pressure being correct and HW stat at max. Temperature rise of 35 degrees C.
Were told the temperature gauge should indicate 70. It did.” Same temperature display Flowmatic and Biasi 24S

Your suggestion was that copper coil in a steel pot could not be compared to stainless steel heat exchangers which have good thermal heat transfer. Fail to see how you can say that when the Excel uses same heat exchanger as the Flowmatic but has DHWHE similar to one fitted in Biasi 24S. 70 degree test remains unchanged regardless of type of HWHE used in the two Vokera boilers.

We are not talking about brand spanking new boilers when we debate 70 degree display on OP’s boiler. As to setting the ‘HW stat’ at max, that is the exacting standard I use, already posted, earlier in the debate. If you want to discuss temperature drop across the flow and return on a brand new combi during HE delivery, I am sure we can get that data as well but it would be pointless as thread is to assist the OP with his quandary on a boiler that is not brand spanking new.

Newgas. Gas rate has to be correct in my test (70 degree indication on temp gauge) and HW stat at max regardless of HW HE being steel pot or steel plates. If gas rate is lower than badged figure, at stipulate hot water delivery, temperature display will indicate a lower figure. I suspect you already know this.

There are many guys here (Tony included) with knowledge and experience far greater than mine. Tony is a clever man but on this instance Tony, you are not giving straight answers. I am saying a combi will indicate 70 degrees when delivering badged HW with HW stat at max. My observations are based on what I see on old boilers (which OP’s Biasi 24S is). Tony why do you feel that is not the case. If you can give conclusive answer, then I have learnt something new which adds to my faultfinding skills.

 

[Agile]

I was replying to the OP based on his boielr and I stand by what I said.

However, that was based on a typical boiler setting ( i.e. DHW knob not at max ) and I stand by those figures as I go to a lot of those boilers and as they were sold cheaply water treatment was often not done very well.

You are replying in relation to Vokera boilers. I dont visit as many of those and when I do I find them to be suffering from other faults than dirty water. 20-80 stuck or broken diverter valves and Excells diaphragms and dirty or failed fans.

I have never needed to clean a Vokera secondary heat exchanger. Presumably because they were more expensive and so better installed. Consequently I have never needed to regularly measure operating temperatures within Vokera boilers.

Tony

 

[DP]

I have been a little busy, therefore this debate has been somewhat lacking on my part. Tony states in post 5 of this thread, temperature gauge would not show 70 degrees C during HW delivery if DHW HE was totally clean.
Post 17. I am of the opinion that 70 degrees C indicates correct HW operation.
Post 19. Tony you disagree with what I have said questioning my experience of Biasi 24S (you are right- I do not see many- numbers are minuscule compared to number you see). Also, you state no boiler (that you are aware of) will indicate 70 degree C during normal HW delivery.
Post 26. I quote operation on Vokera Flowmatic and indicate similar operation on Biasi 24 and 28S.
Post 27. Tony you think I am doubting you knowledge of this boiler so you have to make a point that you look at a Biasi on average once every three days. It is further stated that Flowmatic with a ‘pot’ cannot be compared with SS plate heat exchanger fitted in a Biasi. I suspect your answer was ‘off the cuff’ remark since the Excel just like Biasi is fitted with stainless steel HW heat exchanger
Post 35. You are hedging Tony. I am talking of checking boiler operation during servicing, repair even normal operation (normal being a personal preference devoid of position on a scale setting) therefore HW stat is at max, burner rate is as stated, HW delivery is as speced. One person might want to take cool shower, you with HW stat set at normal mid position and someone else with stat against the stop ‘pedal to metal’ position. You feel a new boiler on a clean system will show a differential of 15 to 20 degrees. For education I did just that. Brand new Vaillant Ecotec 837 power flushed and chemically cleaned (7 days). Applied temperature probe to flow pipe (where the Flowmatic, Excel and Biasi temperature sensor is fitted). HW stat at max, hot tap fully open. Temperature on meter pegged at 70 degree C

Tony your final post on this thread does not make sense. The debate is 70 degrees C on the temperature gauge during HW demand. Nothing to do with proving you wrong- it is a debate. That is it. Typical boiler settings- I fail to see how one could use typical values to diagnose a fault. For instance, when checking burner pressure, one has to do this under certain conditions to get a definitive result.
You again mention that I am focussed on Vokeras and quote examples of faults on these boilers (name a boiler that does not suffer from similar defects) which I see as clouding the debate of 70 degree display. Other faults are not relevant. Dirty fans, split diaphragms, broken diverter valve etc are of no consequence.
I have already stated Biasi boiler I repaired/ serviced indicated said temperature. Test yesterday gave same results on a brand new boiler fitted to a clean system.

Tony. Above is not to belittle your vast knowledge. This debate started when you disagreed that a temperature gauge would indicate 70 degrees C during HW. So far you have not said anything definitive why you disagree. I feel a manufacturer will design a boiler with a main heat exchanger that will produce heat that the secondary heat exchanger will ‘sink’ thus results will be very similar between brands and different makes. Cost of appliance is irrelevant as no manufacturer, I would suspect, produce an appliance with mismatched components. I have shown in my postings on this thread, that a Flowmatic with a pot, Biasi with a plate heat exchanger (which is similar to a Flowmatic with plate heat exchanger which the Excel can be taken as) or a modern clean condensing Vailant combi, all give similar results

’70 degrees on gauge’ has enabled me to set the HW flow rate on combis when a Weir gauge is not available.

 

[Agile]

Danny, you have identified a testing senario which is different to mine.

I test a boiler under normal or typical operation, NOT with DHW temp at maximum. Obviously we will get different results doing our tests differently.

Typically I set the DHW temp to about 2/3 - 3/4 of maximum and the flow rate to about 9 li/min for a 24 kW boiler. This will result in the boiler running at or near maximum power and with a 8° C incoming will give about 43° out which is what most users find about right.

I have usually found the "pot" type have a higher differential between system and DHW temperatures. Perhaps thats the design or perhaps thats because they are rather sludged/scaled up which is not surprising as they are now mostly 15-20 years old.

I am rather busy with installation work at the moment but will try to do a few test measurements on a selection of different boilers.

Different boilers have different maximum DHW flow temperatures when the knob is at maximum which is why I set them to typical users settings to be more representative of actual use.

I am told they should now never produce more than 55° under EC regulations. Once went to investigate a customer's complaint that hot water was not hot enough and it was too cold in the bathroom! Turned out she expected kitchen hot water at 70° C to dissolve grease on plates ( presumably without washing up liquid ) had to explain boilers were designed not to scald. The temperature in the bathroom was about 6°C below the temp leaving the boiler because the hot water pipework was old screwed steel running a long way round the house.

Tony

 

[DP]

Tony my fixation is about 70 degrees C temperature of flow pipe. You again say things which have little relevance to the point of 70 degrees which you disagreed with earlier on in the thread.

I question the validity of running a boiler at 2/3 setting for it to give 43 degrees of hot water at the tap. Most manufacturers quote 35 degrees temperature rise, which is correct in your example, but I would like to see how a boiler will achieve this at a normal 2/3 to 3/4 setting when incoming cold water is lowly 8 degrees C.

You keep going back to pot type HWHE. I have quoted three different examples all providing same results

Different boilers have different maximum DHW flow temperatures when the knob is at maximum which is why I set them to typical users settings to be more representative of actual use.

Can you name the boiler?

Do you conceed the point that I was correct when I said primary will be at 70 degrees C when boiler is running at full power during HW demand be it for test purposes or householder choosing to set at full power. Mind, 9.5l passing through a 24Kw boiler will raise the temperature by 35 degrees lower if stat set at a lower setting. Try it out and see.

 

[Agile]

If you set the DHW control to maximum then you can easily get 70° C but then you could get higher or lower as well depending on all the other parameters.

I intentionally set the controls as I do to be comparative so that the temperatures are not variable with inlet water temperatures.

Furthermore, with the control knob set down from maximum if the water flow is not too high then the boiler will be under temperature control which further serves to give comparative operating parameters.

My objective is to test that the boiler is not exhibiting poor temperature transfer and to test that it is controlling the temperature. I also turn the control down to check the power input reduces.

Tony

 

[DP]

Tony how will you get 70 degrees hot water with flow rate of 9.5l per minute with stat at max. This is implying boiler will be capable of raising the temperature by massive 60 degree centigrade now that cold water hereabouts is at 10 degrees C.

What has your setting of controls got to do with it? I thought the sensors did the controlling

Why will a boiler not be in control with stat set at maximum? How can a boiler exhibit poor temperature transfer? Surely, heat output from the main heat exchanger is sunk by the hot water heat exchanger.

Tony can you leave personal preferences out of it as I am looking for answers that I can use in the field. Kind of information I am looking for is - stat at min, themperature probe on flow pipe as it leaves the main heat exchanger and hot tap running at full flow. There is no chance of making a mistake when precise instructions are followed. You may well have personal preferences that allow you to carry out a task successfully but is it a yardstick that can be used in every task be different people?

 

[Agile]

I did not mention 9.5 li/min because I set it to about 8 li/min at this time of year. At that flow rate the boiler will be under temperature control by modulating back slightly. I am wanting to test that it is controlling the output temperature by modulating back and that the boiler flow temperature is not excessive as would be caused by a blocked or poor thermal transfer in the plate HE.

If you set the water temp to maximum then the boiler is constrained by its set max power input. That is what you are doing which is different from how I test that boilers are working properly after any repairs or servicing. I will always have set the min/max gas pressures before this.

I need to be sure the boiler will work properly in normal useage with normal settings. I show the settings to the client and advise them they can adjust the hot temp slightly to suit their preferences. I sometimes have to advise them that a combi should be set to deliver water at close to the temperature to be used. (i.e. Not to add lots of cold water ).

There is also a situation where the thermal transfer is poor in the HE but the flow rate is not reduced. That can result in elevated primary temperatures but still achieve normal heating of the secondary water. That results from a thin oxide coating on the primary transfer surfaces.

Tony

 

[DP]

I did not mention 9.5 li/min because I set it to about 8 li/min at this time of year

Tony, you did not say 9.5l or 8l. Above is what you said.

At that flow rate the boiler will be under temperature control by modulating back slightly. I am wanting to test that it is controlling the output temperature by modulating back and that the boiler flow temperature is not excessive as would be caused by a blocked or poor thermal transfer in the plate HE.

So ineffect, at a flow rate of 8l per minute, you are allowing the water to stay in the HW heat exchanger longer resulting in higher temperature, which you then control by reducing the HW thermostat setting to effect control. End result bath fills in not 15 minutes but takes even longer. Why do you assume every HW heat exchanger is blocked or has poor thermal heat transfer?

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?

I need to be sure the boiler will work properly in normal useage with normal settings. I show the settings to the client and advise them they can adjust the hot temp slightly to suit their preferences. I sometimes have to advise them that a combi should be set to deliver water at close to the temperature to be used. (i.e. Not to add lots of cold water ).

Not any different from what anyone else would do.

There is also a situation where the thermal transfer is poor in the HE but the flow rate is not reduced. That can result in elevated primary temperatures but still achieve normal heating of the secondary water. That results from a thin oxide coating on the primary transfer surfaces.

What I make of this statement is as follows. Heat generated by main heat exchanger is not absorbed by HWHE, So temperature starts to rise on the PRIMARY side because absorption of heat instead of theoretical 100% is now let us say 90% due to oxidation of HWHE. So, what will the temperature gauge display under this condition? Over 70 degrees C I presume?