Frozen pipe in extension

Section62

grumbler said:

Section62 said:

ThisIsWeird said:

Your best bet is the fan heater, as this will likely get to the frozen area most quickly. Don;t try and warm the whole kitchen, but aim it at the frozen site. The best ways will be from under the sink base cupboard - can you unscrew the plinth? If so, aim it in there so it flows up behind the unit where there will be a gap. Or, is there a washing machine beside the sink base? Pull it out and look in there - any holes or gaps in to behind the sink base? If so, see if a hair dryer can fire a warm blast in there.

As with the running of the hot tap, I wouldn't necessarily have the heaters running full blast, but at a medium setting - give the pipe time to thaw. If that doesn't work in 30 minutes, then blast it!

No, the OP was correct to use a fan heater to gradually warm up the room as a whole.  The idea is to raise the temperature slowly so the ice melts gradually, avoiding a build up of pressure which could burst the pipe.

The worst thing to do with a frozen pipe is to "blast it" with heat - even if the blasting is in the general direction rather than directly on the pipe.  The key word here is 'slowly'.

I don't think there is any physics behind this. Pipes burst because of water expanding when freezing, not because of some pressure 'building up'.

In which case you think incorrectly.

Water has its maximum density (and therefore smallest volume) at 4 degrees C.

It expands both as it cools below 4C and as it heats above 4C.

The danger when frozen water pipes thaw is if both ends of the pipe section are 'closed'.  This can happen for example if there remains an ice 'plug' either side of a section of pipe which is warming up.

Once the water in the central section gets above 4C it will start expanding.  If the ice plugs remain intact (and we all know that they can, hence the use of pipe freezing for repair work) then the pressure in that central section of pipe will increase.  The same applies if there is a closed tap or valve instead of an ice plug.

(The rate of expansion wrt temperature is also greater above 4C than it is below 4C)

Therefore unless care is taken to start thawing a pipe from an outlet which has been proven to be open to the atmosphere (or other expansion space), pressure may be "building up" in the pipe and this may result in a burst.

Pipes can burst because water expands as it freezes, but they can also burst because the thawing water has no pressure release if ice plugs are still present either side of the thawing section.

Natural or slow warming of the whole pipe (i.e. by raising the ambient temperature) minimises the risk of a pipe burst on thawing as it also minimises the risk of intact ice plugs.

grumbler

Section62 said:

grumbler said:

Section62 said:

ThisIsWeird said:

Your best bet is the fan heater, as this will likely get to the frozen area most quickly. Don;t try and warm the whole kitchen, but aim it at the frozen site. The best ways will be from under the sink base cupboard - can you unscrew the plinth? If so, aim it in there so it flows up behind the unit where there will be a gap. Or, is there a washing machine beside the sink base? Pull it out and look in there - any holes or gaps in to behind the sink base? If so, see if a hair dryer can fire a warm blast in there.

As with the running of the hot tap, I wouldn't necessarily have the heaters running full blast, but at a medium setting - give the pipe time to thaw. If that doesn't work in 30 minutes, then blast it!

No, the OP was correct to use a fan heater to gradually warm up the room as a whole.  The idea is to raise the temperature slowly so the ice melts gradually, avoiding a build up of pressure which could burst the pipe.

The worst thing to do with a frozen pipe is to "blast it" with heat - even if the blasting is in the general direction rather than directly on the pipe.  The key word here is 'slowly'.

I don't think there is any physics behind this. Pipes burst because of water expanding when freezing, not because of some pressure 'building up'.

In which case you think incorrectly.

Water has its maximum density (and therefore smallest volume) at 4 degrees C.

It expands both as it cools below 4C and as it heats above 4C.

The danger when frozen water pipes thaw is if both ends of the pipe section are 'closed'.  This can happen for example if there remains an ice 'plug' either side of a section of pipe which is warming up.

Once the water in the central section gets above 4C it will start expanding.  If the ice plugs remain intact (and we all know that they can, hence the use of pipe freezing for repair work) then the pressure in that central section of pipe will increase.  The same applies if there is a closed tap or valve instead of an ice plug.

This is correct, but IIRC ice has the same density as water at +30C(?). So, if the pipe is frozen at its ends, you have to heat it above 30C to get higher pressure than it was when the water was frozen. And don't forget that the pipe expands as well when heated.

Eldi_Dos

If you heat a copper pipe quickly it will expand in all directions making the internal diameter smaller while the ice is still inside pipe thus putting added pressure on pipe is the way I have always viewed this.

Pineapple88

Thank you all. I put the fan heater near the cupboard (with the cupboard door open) so that area started to warn up first and it thawed out after about 30 mins. Luckily the pipe doesn't seem to have burst although given the difficulty accessing it I can't be sure. 

This is the first time that the pipe has frozen so I can only assume its its because it was so cold last night, but as you have pointed out it could easily happen again. Unfortunately all of the pipework is covered up though so I think I will need to cut through the board at the back of the cupboard. Someone mentioned a recess where the dishwasher is - I'm not sure what you mean by this? I only have a kickboard at the bottom and the space behind the sink cupboard (which is covered up)?

grumbler

Eldi_Dos said:

If you heat a copper pipe quickly it will expand in all directions making the internal diameter smaller

Not true.

When you heat a pipe/washer both diameters become bigger.

Even if you manage to heat it so fast, that inner layer remains cold, the outer layer will expand and pull the inner layer out. This is pure theory as copper is one of the best conductors of heat.

ThisIsWeird

Pineapple88 said:

Thank you all. I put the fan heater near the cupboard (with the cupboard door open) so that area started to warn up first and it thawed out after about 30 mins. Luckily the pipe doesn't seem to have burst although given the difficulty accessing it I can't be sure. 

This is the first time that the pipe has frozen so I can only assume its its because it was so cold last night, but as you have pointed out it could easily happen again. Unfortunately all of the pipework is covered up though so I think I will need to cut through the board at the back of the cupboard. Someone mentioned a recess where the dishwasher is - I'm not sure what you mean by this? I only have a kickboard at the bottom and the space behind the sink cupboard (which is covered up)?

Good result - nicely done.

Is the dishwasher a free-standing item, which is slipped under the worktop? If so, if you look down the side against the sink unit, or even pull it out for a better look, there's a chance that there will be holes in the side of the sink base which are positioned behind the back panel. More likely, though, is that all the holes for the supply and waste pipes will be forward of this back panel - you can see these pipes coming inside the sink base? It was mentioned only as a possible way to get a source of warm air directly into that void behind the sink base where the frozen pipes appear to be.

If you take a nice wide photo of the inside of the sink base unit, we can advise on ways of gaining access to behind that panel. I had to do this a few years back when I replaced the tap, as the pipes were located behind the back panel. It was as 'easy' as cutting two vertical lines through the panel, which is usually made of hardboard, to free up a section which could then be pulled forward and out. To replace it, I just glued two strips of hardboard down behind each remaining piece, so it overlapped out by a half-inch. The replaced panel just popped back into place - prevented from falling right back by these two strips - and are held in place with a few pan-head screws, so very easy to remove again if needed.

Usually the back panel sits in a groove in the sink unit base, and at the top just sits against the back rail, with a central screw. So once you make these two vertical cuts, the freed section just falls forward and you lift it out. A bit trickier in reality than described :-)

ThisIsWeird

The description of the way thawing pipes can cause bursts was very interesting, and was something I was completely unaware of. I would need evidence, though, before I'd accept that it was anything other than a very minor cause of bursts - surely the vast majority occur when the water expands as it freezes, and the burst only becomes evident when it thaws out and water can escape?

diystarter7

Hi OP
I don't think anyone has said this but it's worth noting. Please be fully aware of where your stop !!!!!! is and it is fully functioning as
there is always a possibility that pipe/s is fractured and when it thaws, you know the rest so be prepared.

For future needs, I'd seriously consider cutting away the back of the unit to add insulation. Be careful only to cut what is required in order to maintain the integrity of the unit.  Yes, you will see, not the refitted cut out/s but soon forget but miles better than having flood damge or worrying about it every cold spell.

Good luck

Thank

Section62

ThisIsWeird said:

The description of the way thawing pipes can cause bursts was very interesting, and was something I was completely unaware of. I would need evidence, though, before I'd accept that it was anything other than a very minor cause of bursts - surely the vast majority occur when the water expands as it freezes, and the burst only becomes evident when it thaws out and water can escape?

I don't think anyone keeps those statistics, but Thames Water (who ought to know what they are talking about) put the emphasis on cases where the burst happens as the temperature rises -

During cold weather, the pipes in your home can freeze and then when the temperature rises there’s a chance a frozen pipe may crack or burst. Don’t worry, our tips and advice should help in these situations.

https://www.thameswater.co.uk/help/emergencies/frozen-or-burst-pipes

I thought it was well known by professionals and knowledgeable DIYers that rapid thawing of frozen pipes was a significant cause of bursts... another schoolday for me.

ThisIsWeird

Section62 said:

ThisIsWeird said:

The description of the way thawing pipes can cause bursts was very interesting, and was something I was completely unaware of. I would need evidence, though, before I'd accept that it was anything other than a very minor cause of bursts - surely the vast majority occur when the water expands as it freezes, and the burst only becomes evident when it thaws out and water can escape?

I don't think anyone keeps those statistics, but Thames Water (who ought to know what they are talking about) put the emphasis on cases where the burst happens as the temperature rises -

During cold weather, the pipes in your home can freeze and then when the temperature rises there’s a chance a frozen pipe may crack or burst. Don’t worry, our tips and advice should help in these situations.

https://www.thameswater.co.uk/help/emergencies/frozen-or-burst-pipes

I thought it was well known by professionals and knowledgeable DIYers that rapid thawing of frozen pipes was a significant cause of bursts... another schoolday for me.

How many pipe bursts do you think are caused by thawing as opposed to the initial freezing?

In any event, a bust pipe will usually only become evident once the pipe has thawed out.

A schoolday for me too.