My plumbing's all wrong...

[KarlosMacronius]

Hello all,

 

I recently reinstalled my calorifier and plumbing during a major refit. There are only 4 outlets on the calorifier an inlet and outlet for engine coolant and and inlet and outlet for water. Before disconnecting anything I was very careful to note whiche pipes went where and noted 'cold in' and 'hot out' on the corresponding in/outlets. (there is additionally an outlet that has always been a bleed valve that was never touched)

 

Its all connected up fine and is pretty much the same set up as before just with new piping. But I've noticed a few things that are different.

 

The first thing I have noticed is the water pump runs for longer than before and takes longer to come on than before, this I assume means the accumulator is doing a better job for some reason? but this is trivial compared to the other thing...

 

The cold taps are hot...and so are the hot taps.

 

 

why might this be happening now when it wasn't before? I have the same fittings (bleed valves, stop cocks etc) as before in the same configuration.

I assume that for some reason both taps are drawing water from the calorifier, or worse ALL the water in the boat is somehow being heated possibly including my water tank (not a great idea)

 

An easy fix would presumably be to install a one way valve (if these exist in push fit form) in the cold feed just before the calorifier. But I would rather understand why this is happening...

 

Any suggestions are much appreciated.

[by'eck]

An airlock in the cold feed to the calorifier would explain the pump running longer than normal.

 

If a non-return valve (NRV) is already fitted to this feed I guess there is a small possibility the air lock could compromise its operation, allowing hot water back into the cold system. A correctly working one would certainly avoid this.

 

If no NRV then maybe the pressure release valve (PRV) on the calorifier has accidentally been tweaked higher than before so instead of releasing excess pressure its forcing water back into cold system. Some fit an expansion vessel on the hot outlet feed to control this pressure until a hot tap is opened.

 

Finally you may have accidentally messed up the plumbing although from what you have said that seems unlikely.

[David Mack]

Does the feed to the hot taps exit the calorifier right at the top, or part way down?

 

If its the latter, then you could have a load of air in the top of the calorifer. The pump compresses this, so it acts as an accumulator, but when you open a tap (hot or cold), this air expands and pushes hot water out of whichever tap you have opened. If you leave the cold tap running for long enough it would then run cold.

 

You need to see if you can bleed the calorifier.

[KarlosMacronius]

I will check for an airlock and attempt to rectify it if there is one.

 

There's currently no NRV fitted.

 

I wasn't aware that the PRV might be adjustable, I'm pretty sure the one fitted (in the hot pipe close to it coming out the calorifier) states a pressure on it so I assumed it would always operate at this pressure (I cant remember what pressure it is off the top of my head maybe 4 bar?) How do you adjust a PRV that can be adjusted? this seems like the most likely possibility as I sit at work.

 

An expansion vessel may be worth considering but surely that would only postpone the hot water backing up the cold pipes rather than solve it.

 

I assumed the error was mine at first but tracing it all back it seems correct... and hot coming out of both taps seems to indicate a back flow of some sort as the cold tap is on a spur between the water tank and calorifier.... I will check again though. Twice.

 

I may draw a diagram of the set up and post it tomorrow if that would help...

[Kae]

Your calorifier is full of air, that's all.

A non return valve (check valve) in the cold entry pipe will stop the back syphoning of hot water into your cold supply.

[by'eck]

I will check for an airlock and attempt to rectify it if there is one.

 

There's currently no NRV fitted.

 

I wasn't aware that the PRV might be adjustable, I'm pretty sure the one fitted (in the hot pipe close to it coming out the calorifier) states a pressure on it so I assumed it would always operate at this pressure (I cant remember what pressure it is off the top of my head maybe 4 bar?) How do you adjust a PRV that can be adjusted? this seems like the most likely possibility as I sit at work.

 

An expansion vessel may be worth considering but surely that would only postpone the hot water backing up the cold pipes rather than solve it.

 

I assumed the error was mine at first but tracing it all back it seems correct... and hot coming out of both taps seems to indicate a back flow of some sort as the cold tap is on a spur between the water tank and calorifier.... I will check again though. Twice.

 

I may draw a diagram of the set up and post it tomorrow if that would help...

 

Many aren't but on my last boat it was. Worth checking regularly its working.

 

When I said air lock in the cold water feed I mean't most likely in the calorifier itself BTW.

[KarlosMacronius]

AHA! that makes sense. The calorifier is positioned lying down with all the pipe work coming from one end (which would be the top if you stood it up I guess) including the bleed valve so I will up end it and bleed thoroughly.

 

Thanks for the advice everyone!

[bottle]

Horizontal calorifier are known to be a pain in the posterior for getting all the air out.

 

Good luck

[SamKingfisher]

I fitted a bleed valve in my horizontal cauliflower. Have had to use it twice now.

[Bobbybass]

You should still have a non-return valve.

 

As the calorifier heats up..the water will expand and force back out into the cold system.