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

[Millsy 82]

It will be fine just use your heating like normal get some one out to fix your tap and then your be back running like normal.

 

[Millsy 82]

If its the ferroli Im thinking of then the ch and dhw pipework run through the same heat exchanger, such that if you turn off the cold feed to the boiler, the hw side will run dry or part dry, so there is a risk of the remnants in the hex to boil away and even pressurise up as stem if things go wrong. In this situation you should leave the hot in let and oulets open to avoid hex problems, being thats going to be a pain in the bum, just dont use the boiler till the taps repaired, simples and cheapest option. Saves you getting a popping and hissing noise from the boiler

You do realise that water boils at 100c and I have not yet come across a boiler that heats up to 100c in normal operation so I cannot see the problem. If anything it would cause more of a problem when its full of water as the water has to expand so I think your sprouting absolute rubbish.

 

[dancinplumba]

You do realise that water boils at 100c and I have not yet come across a boiler that heats up to 100c in normal operation so I cannot see the problem. If anything it would cause more of a problem when its full of water as the water has to expand so I think your sprouting absolute rubbish.

think lame is saying that any water left in dhw side will expand in the heatex from the ch side as its dualpass and this could cause probs unless a tap is opened, as op says hot tap is stuck open there will be no probs imho

 

[lame plumber]

I'll try to explain why I gave the advice I did

if the water is running through the hex it wont boil stage 1.
but if the water is not moving and just sitting there theres a good chance its going to get hotter than planned stage 2
which is why low water content boiling are prone to problems when you allow this to happen stage 3

so you never want a situation where the waters able to potentially boil, which is why the likes of chris brown from ferrolli spends most of his time going out to new installs where the installer has failed to prime the water pump and the water in the hex boils melting the flow switch and blowing all the o ring seals on the boiler.

Prehaps thats why I would advice you not to use a boiler with your problem unless you open up the inlet/outlet to prevent risk of boiling.

and dancin got there first again

 

[Reg Man]

Dual heat exchanger in the older models. so if you loose your cold water to the hot water side it will cook nicely. Best advice is do not use without a cold water supply. No service valve up to the offending tap then?

 

[Millsy 82]

think lame is saying that any water left in dhw side will expand in the heatex from the ch side as its dualpass and this could cause probs unless a tap is opened, as op says hot tap is stuck open there will be no probs imho

I still think hes sprouting rubbish as its usually full of water at mains pressure so I cant see the problem the boiler has an overheat which will stop it boiling and the heat exchanger is designed to with stand the pressure of mains water.

 

[dancinplumba]

see your point but stat will only kick in if ch water gets too hot imo

 

[tom609]

hi everyone i'm new to the site i agree with dancin on this will be ok

 

[Reg Man]

Overheatstat will kick in on this boiler, at 80degrees "with any luck". But this is a distressing fault condition temperature for the poor old heat exchanger. Why take the risk? Could right off the boiler for the sake of waiting for a tap repair.

 

[lame plumber]

I still think hes sprouting rubbish as its usually full of water at mains pressure so I cant see the problem the boiler has an overheat which will stop it boiling and the heat exchanger is designed to with stand the pressure of mains water.

but you just hit the nail on the head there, mains is off as the tap is leaking so its not at mains pressure, so water can boil at 100 deg c and lack of water can let it boil, produce steam which can be quite high pressure which can also damage the o rings and cause leaks. Hence why all low water content boiler have overrun to cool the hex to prevent hot spots etc cooking them. So the only one spouting rubbish is milsy

 

[Nostrum]

How can high pressure steam be produced when the tap is open

 

[lame plumber]

How can high pressure steam be produced when the tap is open

bit of water left in the pipework (clutching at straws here ), but the main issue is you could fairly easily cause damage when there no need to if you dont use the boiler, why risk it??

 

[dancinplumba]

hi everyone i'm new to the site i agree with dancin on this will be ok

hi tom introduce yourself here New Member Introductions

 

[dancinplumba]

but you just hit the nail on the head there, mains is off as the tap is leaking so its not at mains pressure, so water can boil at 100 deg c and lack of water can let it boil, produce steam which can be quite high pressure which can also damage the o rings and cause leaks. Hence why all low water content boiler have overrun to cool the hex to prevent hot spots etc cooking them. So the only one spouting rubbish is milsy

the ch side is still full of water and will dissipate the latent heat in the hex

 

[Reg Man]

How can high pressure steam be produced when the tap is open

No it will just boil the heat exchanger dry. Oh we still have the overheat stat. I wonder what the boilers potentiometer will think of this.

 

[lame plumber]

would any of the leave it its ok, who have a ferrolli like this at home, pop out and set it up to see what happens in this situ and let us know pse

 

[dancinplumba]

would any of the leave it its ok, who have a ferrolli like this at home, pop out and set it up to see what happens in this situ and let us know pse

or a junior

 

[stevetheplumber]

its safe to leave the heating running even with no mains feed it will only fier for heating and the water flow keeps the hex at normal temps and pump will over run to dissipate het when boiler goes of

 

[lame plumber]

forgot, plumbers dont work on sundays unless callouts £200 plus :sleeping:

 

[Millsy 82]

There is no way that the boiler firing up for heating is going to cause any damage to the heat exchanger because the DHW side is empty The pump will run and this will take the heat out of the boiler. Yes there is still going to be water in the DHW side but at zero pressure it will not build up so drastically that it is going to cause damage to the heat ex. As for the OH stat it will also cut the boiler out on the DHW side of things as well as the heating it is a safety feature that will shut the boiler off when heat exchanger gets to a set temperature. It will not do any thing to the potentiometer as every OH stat I have ever come across in the 14 years I have worked in this trade work the same they go from closed to open circuit.

I have left many peoples heating running in the past whilst I have had the water off changing taps etc and surprise surprise I have never killed anybodys heat exchanger. I would suggest Lame plumber that you do not comment on things you are 100% sure of as in this case you are definately sprouting rubbish.

 

[lame plumber]

we can all have an opinion, but there's no need to be rude, after all forums are for discussion and everyone has had different experience of boilers and problems and because of issues I have had, esp with a ferrolli in the past I offered my opinion such that the bloke posting a query could make a choice. Like I said, I've experienced a ferrolli doing just this when I failed to bleed a pump thro recently, it only wrecked a couple of o rings but when chris from ferrolli turned up, he was decent enough to point out loads of his work involves repairing boilers where the hex is boiled and o rings blown and flow valves melted, and with that damage pcbs etc knackered. This is being done regularly on new installs so there is the potential to do the same with this boiler if your luck runs out so why risk it. So as you tried to say, you shouldnt comment on things you are not 100% sure of, but in this case I'm 98% sure so I think I can offer an opinion without being told I'm sprouting, sorry spouting a lot of rubbish. If you want to comment, please feel free, its an open forum but dont get arsy as its not really needed. After all the guy only wants an opinion to make his choice! be it yours or mine or someone elses

 

[Billy Bob Bob]

There is no way that the boiler firing up for heating is going to cause any damage to the heat exchanger because the DHW side is empty The pump will run and this will take the heat out of the boiler. Yes there is still going to be water in the DHW side but at zero pressure it will not build up so drastically that it is going to cause damage to the heat ex. As for the OH stat it will also cut the boiler out on the DHW side of things as well as the heating it is a safety feature that will shut the boiler off when heat exchanger gets to a set temperature. It will not do any thing to the potentiometer as every OH stat I have ever come across in the 14 years I have worked in this trade work the same they go from closed to open circuit.

I have left many peoples heating running in the past whilst I have had the water off changing taps etc and surprise surprise I have never killed anybodys heat exchanger. I would suggest Lame plumber that you do not comment on things you are 100% sure of as in this case you are definately sprouting rubbish.

sorry but your wrong,end of argument,as said this boiler has a twin pass heat exchanger,there is a risk that remnants of water left in the domestic side can cause issues if the ch is used,now who has the balls to argue differently with me about boiler design??? i am not taking anyones side but this is FACT

 

[dancinplumba]

we can all have an opinion, but there's no need to be rude, after all forums are for discussion and everyone has had different experience of boilers and problems and because of issues I have had, esp with a ferrolli in the past I offered my opinion such that the bloke posting a query could make a choice. Like I said, I've experienced a ferrolli doing just this when I failed to bleed a pump thro recently, it only wrecked a couple of o rings but when chris from ferrolli turned up, he was decent enough to point out loads of his work involves repairing boilers where the hex is boiled and o rings blown and flow valves melted, and with that damage pcbs etc knackered. This is being done regularly on new installs so there is the potential to do the same with this boiler if your luck runs out so why risk it. So as you tried to say, you shouldnt comment on things you are not 100% sure of, but in this case I'm 98% sure so I think I can offer an opinion without being told I'm sprouting, sorry spouting a lot of rubbish. If you want to comment, please feel free, its an open forum but dont get arsy as its not really needed. After all the guy only wants an opinion to make his choice! be it yours or mine or someone elses

nothing to do with the dhw side then ??

 

[dancinplumba]

sorry but your wrong,end of argument,as said this boiler has a twin pass heat exchanger,there is a risk that remnants of water left in the domestic side can cause issues if the ch is used,now who has the balls to argue differently with me about boiler design??? i am not taking anyones side but this is FACT

how and why ?

 

[Nostrum]

Ok, so whats the difference between this and the heat exchanger on the DHW side being full as you would find in normal operating circumstances? So for example, the heating has been on all night and no one has run the tap. Late at night the tap is run. The water in the DHW side does not get anywhere near boiling point otherwise it would be lethal as it comes out the tap (the volume of water contained within the heat exchanger all night)

The reason is because the heating side is dissapating the heat, which is exactly the reason why the heat exchangers are joined. If there were 2 completely seperate heat exchangers being primarily and directly heated by the burner then this would occur. Remember this is a heat exchanger and its primary purpose id to be able to transfer heat efficiently. Having a twin pass means the 2 act like a big heat sink to one another.

The reason (in my opinion) lame plumber, you had said problem is because you had no flow in either DHW or heating, therefore no way of dissipating that heat, the boiler cannot react quick enough to shut down so the static water boils (or as near as)