Hot water system

[PaulRainbow]

Expansion is throughout though

Not usually. There is usually a non-return valve on the calorifier inlet, to stop how water expansion forcing hot water through the cold taps. Therefore, expansion only happens on the hot circuit, hence the expansion tank is fitted on the hot outlet.

 

[stelican]

Not usually. There is usually a non-return valve on the calorifier inlet, to stop how water expansion forcing hot water through the cold taps. Therefore, expansion only happens on the hot circuit, hence the expansion tank is fitted on the hot outlet.

Yes of course only meant expansion on the hot side. but needs a pressure relief valve.

 

[Timeless 2]

Cold water storage tanks deforming and collapsing in the loft was not that unusual up to the 80s when regulations were changed to have a hi limit thermostat installed built into the immersion stat. Still come across them now and again on back up immersion heaters that don’t get used for decades.
With the valve installed I have seen them on the cold inlet and hot outlet. They only work on pressure which would be the same hot or cold. There are temperature and pressure relief valves that are installed into a hot water tank and work on excess temperature and pressure but that’s not one.

 

[Seastoke]

I'm doubting that story tbh. Excepting some very shoddy plumbing.

Cold water storage tanks have an overflow built in to prevent just such a scenario. This is usually a pipe out under the eaves, or to some other outlet. Of course if somebody cut corners and didn't fit an overflow, as you were.

You miss the point the water got hot and the tank buckled .

 

[Seastoke]

Right this is a true story, when there used to hot tanks in houses, if the immersion heater over heated it had a expansion pipe that put hot water back into the cold water tank in the loft , in one situation the hot water made the cold tank soft with it being plastic , the tank buckled and hot water scalded a child in bed.

I'm doubting that story tbh. Excepting some very shoddy plumbing.

Cold water storage tanks have an overflow built in to prevent just such a scenario. This is usually a pipe out under the eaves, or to some other outlet. Of course if somebody cut corners and didn't fit an overflow, as you were.

Ok you are calling me a liar , so if you Google from 2008 young girl scalded to death from hot water , read the story then apologise .

 

[markc]

Ok you are calling me a liar , so if you Google from 2008 young girl scalded to death from hot water , read the story then apologise .

Really horrific incident. Probably best not to actually read it.

 

[Seastoke]

Not usually. There is usually a non-return valve on the calorifier inlet, to stop how water expansion forcing hot water through the cold taps. Therefore, expansion only happens on the hot circuit, hence the expansion tank is fitted on the hot outlet.

Paul a unvented system needs a pressure relief.

 

[stelican]

Not usually. There is usually a non-return valve on the calorifier inlet, to stop how water expansion forcing hot water through the cold taps. Therefore, expansion only happens on the hot circuit, hence the expansion tank is fitted on the hot outlet.

Don't you mean relief valve on hot side (calorfier)

 

[Seastoke]

Really horrific incident. Probably best not to actually read it.

True, but if the op swaps his for a butterfly , it would be dangerous.

 

[Clash]

Ok you are calling me a liar , so if you Google from 2008 young girl scalded to death from hot water , read the story then apologise .

I'm not calling you a liar. Please don't misrepresent what I said and then demand an apology on the back of a misrepresentation. We could get into an ever decreasing apology spiral until we disappear up our own fundaments. (at least I hope they're our own and we don't swap)

 

[Seastoke]

I'm not calling you a liar. Please don't misrepresent what I said and then demand an apology on the back of a misrepresentation. We could get into an ever decreasing apology spiral until we disappear up our own fundaments. (at least I hope they're our own and we don't swap)

Clash when you doubt someone , you think they are telling a lie but cannot prove it. Now I have provided the evidence it’s true, so should apologise , or it’s pistols at Bristol.

 

[Clash]

Clash when you doubt someone , you think they are telling a lie but cannot prove it. Now I have provided the evidence it’s true, so should apologise , or it’s pistols at Bristol.

I also said there could be a situation that it would happen. Maybe read all I said and not just the first couple of words.

And your some man to be taking pot shots at me, having questioned me about my bona fides with absolutely no basis.

 

[Seastoke]

Personally I think you have embarrassed ones self . I won’t carry on this conversation , I just want the guy to understand safety and get his boat working.

 

[Clash]

Personally I think you have embarrassed ones self . I won’t carry on this conversation , I just want the guy to understand safety and get his boat working.

That's fair enough. But the issue with the boat has nothing to do with thermostats and overflowing header tanks.

In fact the boat is in an unsafe state with a PRV being used to fill the hot water tank instead of its proper task of releasing over-pressure safely. As I said earlier, the PRV should be on the hot side and a butterfly valve on the cold side.

 

[PaulRainbow]

Paul a unvented system needs a pressure relief.

I know that, see post #59

 

[PaulRainbow]

Don't you mean relief valve on hot side (calorfier)

See #59

 

[stelican]

See #59

 

[PaulRainbow]

No idea what that's supposed to mean.

There is usually a non return valve on the calorifier intake, to stop hot water going back to the cold circuits and coming out of the cold taps. An accumulator is usually fitted just after the pump.

On the hot side there should be an expansion tank to cater for expansion caused by heating the water. If the expansion tank is unable to prevent the pressure exceeding the set pressure of the PRV the PRV will open and release some pressure.

As you said, the PRV does not have to be at the top of the tank, but it could be. It can also be at the bottom, if it's between the non-return valve and the calorifier.

The system must have a PRV and should have an expansion tank.

 

[PaulRainbow]

Taking a closer look at the picture in #23

The PRV is in the correct place, just installed incorrectly.

When the PRV is manually operated it is allowing cold water to flow into the calorifier, the pump operates and pressurises the calorifier, then stops. Water will then flow from the hot taps until the pressure in the hot system has gone, then no more water. Just as the OP describes.

The cure is to fit a tee to the calorifier and connect the cold inlet to one branch and the PRV to the other. The end currently fitted to the tank should be fitted to the tee and the end connected to the cold supply should either be open, or have an open ended pipe routed to the bilge, overboard etc.

When disassembling the pipework look for a non return valve. If one is fitted it must be in a position before the PRV. That's in the cold inlet, so the PRV is between the NRV and the calorifier. That way, any excess pressure cannot get back into the cold system, it has to be expelled from the PRV.

 

[stelican]

No idea what that's supposed to mean.

There is usually a non return valve on the calorifier intake, to stop hot water going back to the cold circuits and coming out of the cold taps. An accumulator is usually fitted just after the pump.

On the hot side there should be an expansion tank to cater for expansion caused by heating the water. If the expansion tank is unable to prevent the pressure exceeding the set pressure of the PRV the PRV will open and release some pressure.

As you said, the PRV does not have to be at the top of the tank, but it could be. It can also be at the bottom, if it's between the non-return valve and the calorifier.

The system must have a PRV and should have an expansion tank.

If you closely look at photo in post 33 you will notice that the inlet fitting appears to be a combined Inlet /PRV and drain valve.
please also see me request for advice re 240v power supply.