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jonifresh2008
Junior Member
Joined: 19 Mar 2008
Posts: 5
Location: UK
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 Posted: Wed Mar 19, 2008 7:14 am Post subject: Cold water on sealed system |
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Hi,
Is it ok to run the keep the central heating running on a combi boiler while the main cold water feed is temperary turned off to change a tap.
Thanks |
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ultimatehandyman
Site Admin
Joined: 16 Jul 2005
Posts: 9740
Location: Darwen, Lancashire
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| Posted: Wed Mar 19, 2008 7:18 am Post subject: |
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Yes, that should not be a problem at all.
When you restore the mains water make sure you open the cold taps in the hose first, incase a slug of dirty water is released when you open the stop tap. This way it will not get into the combi 
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jonifresh2008
Junior Member
Joined: 19 Mar 2008
Posts: 5
Location: UK
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| Posted: Wed Mar 19, 2008 8:22 am Post subject: |
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| Thanks for your help. |
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Wed Mar 19, 2008 10:50 am Post subject: |
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You sure about that bossman, I don't think I would be happy.
What boiler is it |
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ultimatehandyman
Site Admin
Joined: 16 Jul 2005
Posts: 9740
Location: Darwen, Lancashire
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| Posted: Wed Mar 19, 2008 5:09 pm Post subject: |
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| thescruff wrote: |
You sure about that bossman, I don't think I would be happy.
What boiler is it |
Why would you not be happy?
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Wed Mar 19, 2008 5:43 pm Post subject: |
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| ultimatehandyman wrote: |
| thescruff wrote: |
You sure about that bossman, I don't think I would be happy.
What boiler is it |
Why would you not be happy? |
I don't know, and I'm too busy today to check 
Combi boilers don't like it if they're running on empty, and I can imagine all sorts of nasty's going on.
If you turn the mains off and open the hot tap to change it, will the diverter valve stick in the hot water mode, and overheat.
Just didn't sound like a good idea. and it still don't, perhaps one of the others can comment |
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gasspark
Senior Member
Joined: 30 Dec 2007
Posts: 143
Location: Liverpool
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| Posted: Wed Mar 19, 2008 5:53 pm Post subject: |
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| thescruff wrote: |
| ultimatehandyman wrote: |
| thescruff wrote: |
You sure about that bossman, I don't think I would be happy.
What boiler is it |
Why would you not be happy? |
I don't know, and I'm too busy today to check
Combi boilers don't like it if they're running on empty, and I can imagine all sorts of nasty's going on.
If you turn the mains off and open the hot tap to change it, will the diverter valve stick in the hot water mode, and overheat.
Just didn't sound like a good idea. and it still don't, perhaps one of the others can comment |
A combi is a sealed system, so is not affected when the water mains is turned off, there just will be no hot water. The UHM's advise is fine.
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Wed Mar 19, 2008 5:58 pm Post subject: |
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But what will happen when you drain the plate heat ex out.
I know you can turn the water off |
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ultimatehandyman
Site Admin
Joined: 16 Jul 2005
Posts: 9740
Location: Darwen, Lancashire
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| Posted: Wed Mar 19, 2008 6:01 pm Post subject: |
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| thescruff wrote: |
But what will happen when you drain the plate heat ex out.
I know you can turn the water off |
Drain what 
He just said he wanted to change a tap washer
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gasspark
Senior Member
Joined: 30 Dec 2007
Posts: 143
Location: Liverpool
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| Posted: Wed Mar 19, 2008 6:10 pm Post subject: |
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You can still change the tap with the heating on the plate heat exchanger will just be empty the heating circuit that passes through the PHE cannot affect the DHW circuit.
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scoobydoo
Junior Member
Joined: 03 Nov 2007
Posts: 23
Location: uk
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| Posted: Sun Mar 23, 2008 12:53 pm Post subject: combi |
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I think scruffs lost the plot,no problem with turning mains off 
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Sun Mar 23, 2008 1:15 pm Post subject: Re: combi |
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| scoobydoo wrote: |
| I think scruffs lost the plot,no problem with turning mains off |
Are you a member of the Kennel Club Scoobydoo 
Suppose there was no local isolating valves on the taps, then the secondary water in the boiler will drain out.
There is the possibility the diverter valve will stay in the DHW position.
Some combi's have a tube in the primary heat exchanger for DHW, with no water init would could/will damage it
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Scruff |
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gasspark
Senior Member
Joined: 30 Dec 2007
Posts: 143
Location: Liverpool
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| Posted: Tue Mar 25, 2008 5:42 pm Post subject: Re: combi |
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| Quote: |
Suppose there was no local isolating valves on the taps, then the secondary water in the boiler will drain out. |
The boiler has its own isolation valve, so it does'nt matter if the tap does not, he stated he's changing the hot tap so isolsting the inlet to the boiler he is isolating all dhw taps
| Quote: |
| There is the possibility the diverter valve will stay in the DHW position. |
The diverter works with a differential between positive and negitive pressures, it requires water flow to be able to make a DHW demand
| Quote: |
| Some combi's have a tube in the primary heat exchanger for DHW, with no water init would could/will damage it |
The tube is not on the heat exchanger but on the outlet pipework of the exchanger and is connected to the negitive side of the diverter valve. But understand where you'r coming from, if the diverter was directing the heating circuit around the boiler only, then there would be a problem if the overheat stat was knacked, would could/will damage boiler, but the chance of the diverter being in that position with the water off would be very rare and for the overheat stat knacked as well even rarer, but technically possible.
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thescruff
Senior Member
Joined: 10 Mar 2008
Posts: 5664
Location: Bath
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| Posted: Tue Mar 25, 2008 5:52 pm Post subject: |
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Thank you Gasspark, for explaining that.
As I said I wasn't sure and small domestic boiler are not my line, I could see a potential problem and voiced an opinion.
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gasspark
Senior Member
Joined: 30 Dec 2007
Posts: 143
Location: Liverpool
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| Posted: Tue Mar 25, 2008 7:32 pm Post subject: |
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No probs, sorted
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