Is a combi boiler safe with NO mains cold water? (Urgent)

[Billy Bob Bob]

how and why ?

the domestic circuit runs through but not in direct contact with the primary circuit(ch) the hex is a direct heat design,as apposed to the plate heat set up that is a indirect heat design,take a polystyrene cup,put a tiny amount of water in it and place your gas lamp on full and torch the bottom,you then get some idea of what your doing to a twin pass heat exchanger when running it in heating mode with no water in the secondary (dhw) circuit only in this cup the water quickly evaporates and the cup melts,in a boiler the small amount of water turns to steam melting o rings,the plastic gubbins of the flow switch,and very quickly the copper tubes within the heat exchanger

 

[chris watkins]

the domestic circuit runs through but not in direct contact with the primary circuit(ch) the hex is a direct heat design,as apposed to the plate heat set up that is a indirect heat design,take a polystyrene cup,put a tiny amount of water in it and place your gas lamp on full and torch the bottom,you then get some idea of what your doing to a twin pass heat exchanger when running it in heating mode with no water in the secondary (dhw) circuit only in this cup the water quickly evaporates and the cup melts,in a boiler the small amount of water turns to steam melting o rings,the plastic gubbins of the flow switch,and very quickly the copper tubes within the heat exchanger

Still don't understand the above ?

Long & short of it is - do we think that a boiler manufacturer (even Ferroli) would design a combi boiler that if the mains water supply was interrupted due to say, water board turning off or a burst pipe, when the heating was on & it would cause damage or failure of heat exchanger ? I don't think so ! I can just see the claims rolling in now, Although not an every day occurrence common enough for the industry to hear about it.

 

[Billy Bob Bob]

i give up

 

[lame plumber]

:77:........

 

[dancinplumba]

lets see if op comes back tomorrow and says because of the advice given here my heatex is buggered ? any bets ?

 

[dancinplumba]

:77:........

YouTube

 

[Nostrum]

Lets all just agree to disagree but we were right and you were wrong? Sounds fair to me

 

[dancinplumba]

Lets all just agree to disagree but we were right and you were wrong? Sounds fair to me

here here

 

[Reg Man]

Lets get this straight, has anyone checked the MI's? I have. This boiler does not have a seperate plate heat exchanger. Its heat exchangers HTG + DHW are both located above an atmospheric burner. So when it calls for HTG it also heats the DHW side regardless of DHW demand. So if the DHW side become empty through evaporation because the water is turned off then the consequences could cause damage.

Agree with everyone if it had a seperate plate heat exchanger heated from the main HTG heat exchanger through a diverter valve. Which is the normal for all your Vaillants, Worchesters ect, but not for an old ferrolli Modena.

Also agree that the overheat would probably protect it. but would not rely on it as thats your last line of safety device.

 

[DirksPlumbing]

I am with Dancing. Lets think what can happen:
This boiler would be designed in a way that the water in the HW heatex pipe could get overheated (significantly past 90odd degC) at any situation. The user would open the HW tap, the pressure would drop, the water in the heatex would turn in milliseconds into steam at the usual expansion rate. Lets say the tap is just near the boiler.
1st: the customer could loose his hearing because of gases leaving at above 1bar.
2nd: the customer can suffer severe steam burns.
3rd: the boiler internals might not cope with the rapid pressure increase and the customer gets hit by boiler(parts).

Next thought: How much water is in the HW heatex and how long would that take to superheat at 30kW input. Lets say there would be demand for half an hour. We assume the HW would be functional but not in use. What temperatures do you expect?

I would say this boiler is safe to use without HW. If not then you have to expect it to be unsafe with HW working too.

 

[dancinplumba]

Lets get this straight, has anyone checked the MI's? I have. This boiler does not have a seperate plate heat exchanger. Its heat exchangers HTG + DHW are both located above an atmospheric burner. So when it calls for HTG it also heats the DHW side regardless of DHW demand. So if the DHW side become empty through evaporation because the water is turned off then the consequences could cause damage.

Agree with everyone if it had a seperate plate heat exchanger heated from the main HTG heat exchanger through a diverter valve. Which is the normal for all your Vaillants, Worchesters ect, but not for an old ferrolli Modena.

Also agree that the overheat would probably protect it. but would not rely on it as thats your last line of safety device.

i have and here they are for your perusal

http://www.ferroli.co.uk/wp-content/uploads/brochures/archives/Ferroli F30 B Manual.pdf

 

[Nostrum]

To be honest, blowing up a Ferroli doesn't sound like such a bad idea anyway

 

[dancinplumba]

To be honest, blowing up a Ferroli doesn't sound like such a bad idea anyway

hahaha so true

 

[Reg Man]

i have and here they are for your perusal

http://www.ferroli.co.uk/wp-content/uploads/brochures/archives/Ferroli%20F30%20B%20Manual.pdf

I have the mi's already and have checked it out, as I said in my previous post.

Anyway its only a problem if the DHW side dries up. so as long as there is water in it no problem.

If this faulty tap is below the boiler do you think it will dry out. So waters off tap is on, even if its above the boiler, what if they turn on the kitchen ho****er tap which is likely to be below the boiler. It will drain the heat exchanger just above the gas burner which is happly burning away because the heatings turned on.

 

[DirksPlumbing]

I have the mi's already and have checked it out, as I said in my previous post.

Anyway its only a problem if the DHW side dries up. so as long as there is water in it no problem.

If this faulty tap is below the boiler do you think it will dry out. So waters off tap is on, even if its above the boiler, what if they turn on the kitchen ho****er tap which is likely to be below the boiler. It will drain the heat exchanger just above the gas burner which is happly burning away because the heatings turned on.

I had thought it is understood that the HW pipe has to be designed in a way that it does not reach temperatures above boiling point under any circumstances?

 

[Reg Man]

So would you turn on a boiler with no water in it?

 

[ggman]

If you take a close look at the hydraulic circuit it becomes evident that the DHW heat exchanger is (wet) on the primary circuit and therefore, as long as the pump is working (and it will when CH is working) it won't reach any temperature above the flow temperature, consequently nothing will melt or overheating. When there is a demand for DHW the electronics after evaluating the flow sensor signal will stop the pump and the full power of the boiler will heat up the primary cooled down by the secondary with running cold water.
conclusion: from the design of it Dancinplumba is 100% correct.

 

[chris watkins]

The frost protection will not work if the electricity and/or gas supply to the unit are cut off.
To avoid damage caused by freezing during long shutdowns in winter, it is advisable to drain allwater from the boiler, the tap water and the system water; or drain off just the tap water andadd a suitable antifreeze to the heating system, as prescribed in chap. 2.3.

Above is from page 6 (1.4), now even Ferroli would not put it in print if there was any chance of it recking their boilers now would they.

 

[DirksPlumbing]

So would you turn on a boiler with no water in it?

Was not aware the OP has a second boiler that is empty?

 

[Nostrum]

I love it when Chris joins in as he seems to find these little one liners from nowhere that supply a definitive answer in hard format.

Right, so now that ones put to bed, what else can we argue about....?

 

[chris watkins]

I love it when Chris joins in as he seems to find these little one liners from nowhere that supply a definitive answer in hard format.

Right, so now that ones put to bed, what else can we argue about....?

Well thank you kind sir.

 

[Reg Man]

Sorry everone, could'nt let this one drop, so I have done the homework and spoken to ferrolli technical. They say that if you run the boiler with the could water main turned off then there is a significant risk that the heat exchanger could be damaged. Especially if any hot water draw offs were left turned on.

 

[chris watkins]

Sorry everone, could'nt let this one drop, so I have done the homework and spoken to ferrolli technical. They say that if you run the boiler with the could water main turned off then there is a significant risk that the heat exchanger could be damaged. Especially if any hot water draw offs were left turned on.

So technical man contradicts the manufactures written instructions, well I know which one I would believe !!
Now please, can we put this one to bed now.

 

[Tap dancer]

Having read 73 posts and all disagreeing with each other, the "op" must be totally confused.

BTW I get the gist of what an "op" is (the person who asked the question, I assume) but does "op" actually stand for something?

 

[lame plumber]

Sorry everone, could'nt let this one drop, so I have done the homework and spoken to ferrolli technical. They say that if you run the boiler with the could water main turned off then there is a significant risk that the heat exchanger could be damaged. Especially if any hot water draw offs were left turned on.

I had already mentioned that ferrolli engineer had warned me of this, but other people know better.