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Discuss Is a combi boiler safe with NO mains cold water? (Urgent) in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Lycanfox

Thanks in advance for any replies to this.

Basically this morning a hot tap would not turn off and was gushing hot water. I couldn't find an isolation valve for the tap so had to turn off all the water via the main stopcock. The only worry is a plumber I rung said that without the cold water going to our combi boiler, the heat exchange could melt itself and cause a lot of damage so we had to turn our heating off.

Now correct me if i'm wrong but surely as long as the hot water setting is turned off on the boiler, the boiler should have two different heat exchangers so the hot water one would not melt due to not having any water to heat if it was off, and the heating exchanger works on a closed loop so should also be ok?

Thanks again for any replies, the last thing I want is to destroy my boiler in such a cold winter.

Adam
 
Depends on the boiler
 
Hi and welcome to the forums. You should get a plumber out to fix your tap and then you won't have to worry about your boiler.

I normally switch all boilers off at the spur switch when turning off the mains water to a property.
 
As far as I know it is a Ferroli Combi F30 D (I think). With a dual heat exchange for hot water and then for central heating.
 
Just turn it off at the wall to be safe
 
without stepping on anyone's toes you wont have a problem. it is safe and imo your plumber is wrong, do as system3 says andget a decent plumber to fix your tap
 
He will be out tomorrow ASAP to fix the tap, I was just wondering for the moment.

What is a spur switch by the way? As Ideally I would like to keep my central heating on but the water off.

Hi and welcome to the forums. You should get a plumber out to fix your tap and then you won't have to worry about your boiler.

I normally switch all boilers off at the spur switch when turning off the mains water to a property.
 
Tyvm.

Getting one out tomorrow morning to fix it....bloody old houses!

without stepping on anyone's toes you wont have a problem. it is safe and imo your plumber is wrong, do as system3 says andget a decent plumber to fix your tap
 
He will be out tomorrow ASAP to fix the tap, I was just wondering for the moment.

What is a spur switch by the way? As Ideally I would like to keep my central heating on but the water off.
hi, as said leave it on, you wont have a problem
 
you could isolate the cold to the boiler which will isolate all hot taps and then turn your cold mains back on so you have water.
 
Turn it on, take the chance, have your heat excahnger changed for ÂŁ200-300 in 6 months
leave it off, dont take the chance, save ÂŁ200-ÂŁ300.

I know which one I would do.
 
As far as I know it is a Ferroli Combi F30 D (I think). With a dual heat exchange for hot water and then for central heating.

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
 
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
that model is the modena he
 
I came across a much older model that wasnt condensing with dual hex fm memory, didnt study it in detail as it was going in the scrap pile, anyway dancin hop it and go back to your hot water bottle and pmt, nicking my one good thought of the evening:46:
 
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If it boiled the domestic hot water then it would boil the heating water as well, the boiler won't fire on H/W demand and the heating water circulating will be enough to dissipate the heat providing it is working correctly that is (debatable I suppose being a ferroli)
 
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If it boiled the domestic hot water then it would boil the heating water as well, the boiler won't fire on H/W demand and the heating water circulating will be enough to dissipate the heat providing it is working correctly that is (debatable I suppose being a ferroli)

not if the runs thro the hex are separate supplies.
 
I came across a much older model that wasnt condensing with dual hex fm memory, didnt study it in detail as it was going in the scrap pile, anyway dancin hop it and go back to your hot water bottle and pmt, nicking my one good thought of the evening:46:
think you are the one thats hoppin lol not me
 
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.
 
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.
 
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
 
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
 
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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?
 
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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.
 
see your point but stat will only kick in if ch water gets too hot imo
 
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.
 
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
 
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