Hot water recirculation

[mackos]

Hi Guys
I am installing a hot water re-circulation system. Linked between the hot & cold taps furthest away from the hot cylinder with a bronze recirculation pump, which works well manually. I need to install a timer for the pump but I also need a thermal bypass valve like the Grundfos one but they are quite expensive. Can I use a thermostatic mixer valve as there will only be cold water going in the hot side until it runs hot shutting off the valve. (that's the theory). What do you think.Thanks Mack.

 

[davesparks]

Why is this being connected to the cold? Normally it would be connected back to the cold feed of the cylinder (or secondary return port if fitted)

What is the bypass valve going to be bypassing and what do you need it in place to prevent?

A mixer valve is unlikely to do the job as it is a variable device (hence the term mixer) rather than what you need

 

[mackos]

Hi Dave This is a retro fit.The idea is you drag the cold/cool water from your hot line & dump it down the cold feed which will take it back to the tank.Once the water is hot enough the Grundfos thermal bypass valve will close the link from hot to cold.The Grundfos valves are quite dear which is why I was wondering whether a TMV would work as you can pick these up from B.E.S for twenty quid.Thanks Mack.

 

[snowhead]

So you're using the cold as a return.
What happens when someone tries to draw cold at a tap closer to the cylinder?

I'll answer that, water which is not cold and potentially in the Legionella band.

 

[davesparks]

Hi Dave This is a retro fit.The idea is you drag the cold/cool water from your hot line & dump it down the cold feed which will take it back to the tank.Once the water is hot enough the Grundfos thermal bypass valve will close the link from hot to cold.The Grundfos valves are quite dear which is why I was wondering whether a TMV would work as you can pick these up from B.E.S for twenty quid.Thanks Mack.

When you say the cold feed do you mean any low pressure cold pipe that happens to be nearby or do you mean the actual cold feed to the cylinder?

This doesn't sound like a very good idea at all to be honest!

A mixer valve will not do the same thing as a mixer valve and I really wouldn't mess with the design of what already sounds like a potentially dangerous system as it is.
The grundfoss valve will presumably have an electrical interlock to the pump to prevent it from pumping constantly against a closed valve, and hopefully have a safety system of some kind to prevent the pump running if the valve fails. Otherwise you'll end up with a situation where hot water is being pumped in to the cold water storage tank and, if it's plastic, melting it and dumping a lot of hot water through the ceiling.

 

[mackos]

Hey Guys I didn't ask for an assassination attempt on my recirculation system.These are already out there by major pump manufacturers. ie Grundfos comfort system where the pump (8 watts) is left on & controlled by the thermal bypass valve which on a closed system feeds the water back into the bottom of the hot cylinder. I just wanted to know if I could use a TMV instead to control the flow of hot water as I have had no experience of these valves. Thanks Mack.

 

[Marvo]

All the comments above are aimed at your proposed system, not at you personally so I think 'assassination attempt' is a bit unfair.

 

[davesparks]

Hey Guys I didn't ask for an assassination attempt on my recirculation system.These are already out there by major pump manufacturers. ie Grundfos comfort system where the pump (8 watts) is left on & controlled by the thermal bypass valve which on a closed system feeds the water back into the bottom of the hot cylinder. I just wanted to know if I could use a TMV instead to control the flow of hot water as I have had no experience of these valves. Thanks Mack.

Nobody has attempted to assassinate you, just trying to get to the bottom of exactly how this system works and how best to advise you to proceed with it, it would be irresponsible for us to blindly advise you on something without knowing the precise details and potential failure modes.

Hot water circulation systems have been around for a long long time as you say, but they normally have their own dedicated pipe return back to the hot water storage. What you appear to have described so far is using the existing cold water service pipework instead of a separate pipe to return the water, which is unconventional and sounds quite ill advised.

A TMV won't work, for a start it won't give any control of the pump.

I can't find anything about a grundfoss thermal bypass valve online via a Google search, can you link to the product you are talking about?

 

[snowhead]

NO you cannot safely use any valve other than the Grundfos thermal bypass.

A system such as the O.P describes does exist;

https://www.plumbingsupply.com/grundfoscomfortsystems.html

The Thermal bypass opens and allows water to pass to the cold pipework when the hot water on it's inlet gets below around 40.c.
So in theory the hot water crossing over is minimal.

However on the link half way down there's a warning;
Please note: All brands of instant hot water recirculation systems that do not require a hot water return line can be dangerous.

 

[davesparks]

NO you cannot safely use any valve other than the Grundfos thermal bypass.

A system such as the O.P describes does exist;

https://www.plumbingsupply.com/grundfoscomfortsystems.html

The Thermal bypass opens and allows water to pass to the cold pipework when the hot water on it's inlet gets below around 40.c.
So in theory the hot water crossing over is minimal.

However on the link half way down there's a warning;
Please note: All brands of instant hot water recirculation systems that do not require a hot water return line can be dangerous.

Is that in America? The language appears to be somewhat americanised and I wouldn't be surprised if such systems are allowed over there as they do seem to have a somewhat lax approach to safety in most services

 

[snowhead]

Yes Us, hence 115v pump

 

[davesparks]

Is the OP in merkin land then?

 

[snowhead]

Looks like Cyprus.
He doesn't say he used the Grundfos system, he's just used a bronze circ pump, so probably 240v

From what was not a particularly good idea, to an improvised home made poor idea.

 

[PEG]

...And i suppose,by the sounds of it,it's bye bye stratification,as well...