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Fitting thermostatic mixer to calorifier


Patrick_C

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Hello all, advice please!

I want to fit a thermostatic mixer valve to an existing calorifier.  At some point it will be replaced with one with an integral mixer. All the installation diagrams I've found show the mixer directly attached to the hot water outlet of the calorifier. However, the current calorifier is in a cramped corner so fitting the valve and running the extra cold water pipe to it will be a bit of a nightmare. 

 

Just adjacent to the calorifier I have a nice accessible spot where the cold inlet and hot output run parallel on the 'hot' side of a non-return valve.  So, is there any reason not to fit the mixer valve there?  All I'd have to do is put a couple of tees into the existing pipework.  

 

Advice appreciated - I can't see why putting it at most a metre away from the calorifier would make a difference but you may know different!

 

thanks in advance!

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As long as the hot feed to the TMV is from the main hot supply pipe from the calorifier before any other hot water pipes split off to taps, etc, then it should be fine.

 

Ideally I think you're supposed to have the first metre of hot pipe from the calorifier in copper to prevent it getting distorted if the water goes above about 90C, but mine is plastic and it's been ok. I installed a TMV about a metre from the calorifier outlet because it was more convenient.

 

You might want to fit a Y strainer in the hot water pipe before the TMV because if you're in hard water areas you'll get lots of bits of limescale from the calorifier which will quickly block your TMV.

 

Y strainer. Don't fit it in this orientation!

 

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Edited by blackrose
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2 hours ago, Patrick_C said:

At some point it will be replaced with one with an integral mixer. 

thanks in advance!

 

I don't understand this bit? A TMV is an integral mixer! It mixes hot and cold water to the set temperature to prevent anyone scalding themselves with very hot water. 

 

By the way, don't set it below about 65C otherwise you risk getting Legionnaires in your system. Although we all run warm water when our tanks cool down, the system needs to be regularly flushed with hot water.

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This is really useful thanks, especially about the strainer.  As for the other bit, I mean that when I've got the £££ I'll get a new and smaller calorifier with the TMV attached directly to it.

 

Edited by Patrick_C
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Now wondering if the cold water for the mixer valve has to come off the cold supply *before* the non return valve otherwise I'll be mixing hot with the potentially warm backflow from the calorifier into the expansion vessel. 

 

Or is it better to have it after the non return valve so it's at the same pressure as the hot water it'll be mixed with?

 

Or does it not matter?  

Edited by Patrick_C
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5 hours ago, blackrose said:

 

 

By the way, don't set it below about 65C otherwise you risk getting Legionnaires in your system. Although we all run warm water when our tanks cool down, the system needs to be regularly flushed with hot water.

Can you get them with a higher than 65 maximum? 65 is the maximum of the ones fitted by Surecal but the likes of Screwfix and Toolstation all seem to have a maximum of around 45.

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33 minutes ago, pearley said:

Can you get them with a higher than 65 maximum? 65 is the maximum of the ones fitted by Surecal but the likes of Screwfix and Toolstation all seem to have a maximum of around 45.

 

Perhaps I've got the Legionnaires killing temperature wrong? I thought it was about 60c in which case all TMVs would need to have a higher max output temperature. I'm pretty sure mine is set higher than 65c but I might be wrong.

4 hours ago, Patrick_C said:

Now wondering if the cold water for the mixer valve has to come off the cold supply *before* the non return valve otherwise I'll be mixing hot with the potentially warm backflow from the calorifier into the expansion vessel. 

 

Or is it better to have it after the non return valve so it's at the same pressure as the hot water it'll be mixed with?

 

Or does it not matter?  

 

I don't know, but the cold supply to my TMV comes from upstream of (before) the NRV.

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44 minutes ago, pearley said:

Can you get them with a higher than 65 maximum? 65 is the maximum of the ones fitted by Surecal but the likes of Screwfix and Toolstation all seem to have a maximum of around 45.

 

Yes you're correct. I'd forgotten about that. We had this discussion years ago on the forum. In fact TMVs should correctly be fitted to outlets rather than an entire hot water system. If you do fit a TMV to a calorifier it's best to have a bypass pipe and a couple of isolation valves so that you only use the TMV if you've heated water from your engine and it's likely to be too hot. 

2 minutes ago, Tracy D'arth said:

 The chance of legionnaires on a closed hot water system which  has no open tank exposing the surface to air is small to non existent.  

 

Ok then ignore what I've said. Doesn't the PRV expose the tank to air?

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In our case, our original calorifier had no TMV but being only 2 feet from the bathroom washbasin the water from that tap was bloody hot after a long cruise, especially on the river. So I fitted a TMV to that tap.

 

When the calorifier was replaced if came with a 65° one fitted. However, with the shower being on the opposite side of the bathroom from the calorifier it was a 30+ feet of pipe run meaning that the water had lost some heat, and Jeannette likes it hot. So I removed the TMV and all is well.

 

For the other mixer taps, sink and bidet, there is no TMV but lever in mid position is about correct temperature.

Edited by pearley
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3 minutes ago, pearley said:

For the other mixer taps, sink and bidet, there is no TMV but lever in mid position is about correct temperature.

 

We have never had a TMV, the basins, kitchen sink and showers have 'mixer taps' so we just let the water run into the basin and add cold to suit.

The immersion heater is at 90 degrees so when diluted down in the shower / sink we get plenty of comfortably hot water.

 

I am always hesitant to add complication (failure points) into any system that functions well enough without.

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We've managed with mixer taps on sinks and the shower until now but we now have a small person who will (once lockdown recedes) be visiting so it's really for their safety.  After the engine or eberspacher has been running (it cuts out at 85c) the hot water really is hot.

  • Greenie 1
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We have two thermostatic mixers. There is one near the calorifier output, which is pre-set (ie not adjustable) at 65 degrees, and there is also an adjustable one for the hot tap on the wash basin in the bathroom. This latter is set to the hottest temperature at which you can comfortably hold your hand, making hand-washing much easier.

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I use a separate TMV to mix hot water (from calorifier) and cold, to feed the hot (now warm!) taps for the sink and shower taps in the bathroom, at a fixed and comfortable/safe temperature. The hot water feeds directly to the hot tap on the galley sink, where I use it for washing up and filling the kettle (which saves a lot of gas). So there are three pipes running along the boat: hot, cold and warm. 

 

I also fitted a bypass valve around the TMV, so that I can drain the warm pipes that are downstream of it. (W in the diagram).


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Edited by Scholar Gypsy
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Thanks for all the input and advice - some of the more comprehensive solutions (using multiple mixers and winterising etc) I may return to if/when we do a comprehensive redesign job.

 

On the issue of whether the cold water should be taken off before or after a non-return or pressure-reduction valve, I called Jabsco who in turn called the manufacturer and the advice was to take the cold water feed off *after* the PRV.  The reasoning being that it's better to have the hot and cold water being mixed at the same pressure. The effect of any warm water from the calorifier/expansion tank will be insignificant once the pump starts to run and cold water starts to move into the calorifier and the feed into the mixer valve.

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3 hours ago, Patrick_C said:

Thanks for all the input and advice - some of the more comprehensive solutions (using multiple mixers and winterising etc) I may return to if/when we do a comprehensive redesign job.

 

On the issue of whether the cold water should be taken off before or after a non-return or pressure-reduction valve, I called Jabsco who in turn called the manufacturer and the advice was to take the cold water feed off *after* the PRV.  The reasoning being that it's better to have the hot and cold water being mixed at the same pressure. The effect of any warm water from the calorifier/expansion tank will be insignificant once the pump starts to run and cold water starts to move into the calorifier and the feed into the mixer valve.

 

"Pressure Reduction Valve"?  PRV = pressure relief valve on calorifier systems unless you have for some reason fitted a non-vented mains pressure indirect cylinder. They may use a pressure reduction valve.

 

A typical calorifier PRV (RELIEF) is Td into the hot outlet pipe from the calorfier, not in series with it, so it won't matter where you fit the mixing vale in relation to the PRV.

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Yes, it's a pressure reducing valve which is needed if you have a Jabsco  Sensor-Max or VFlo pump rather than just a non-return valve: see here: https://www.jabscoshop.com/files/USING A HIGH PRESSURE SENSOR-MAX doc550.pdf

 

There is also a PRV (pressure relief valve) on the calorifier.

 

 

Edited by Patrick_C
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1 hour ago, Patrick_C said:

Yes, it's a pressure reducing valve which is needed if you have a Jabsco  Sensor-Max or VFlo pump rather than just a non-return valve: see here: https://www.jabscoshop.com/files/USING A HIGH PRESSURE SENSOR-MAX doc550.pdf

 

There is also a PRV (pressure relief valve) on the calorifier.

 

 

 

Thanks for that. It seems to me such a pump is a bit of a waste of money pressure wise and as the hot water system as drawn will be operating at a lower pressure than the cold. I think that will have implications for the operation of any thermostatic valve and even more for a manual mixing valve like a cheap shower one.

 

To ensure the same pressure in both the hot and cold system I would take the cold feed to the thermostatic mixing valve from the low pressure side of the reducing valve. That will be the calorifier inlet side.

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No PRV on this system, but there it a non-return valve on the inlet to the calorifier, to stop back-feed of hot water from the calorifier as it heats up. I fed the cold port of the TMV from the outlet of the NRV, so that the pressure on both TMV inlet ports is the same, and to avoid a sneak backwards path around the NRV via the TMV.

 

MP.

 

 

 

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8 minutes ago, Tony Brooks said:

It seems to me such a pump is a bit of a waste of money pressure wise and as the hot water system as drawn will be operating at a lower pressure than the cold

Yes, to be honest its been a bit of a pain in the neck (interesting that Jabsco no longer make the 'electronic' pumps and have no plans to replace them, apparently) and when it finally gives up the ghost I have a simpler pressure-switch pump and accumulator ready to swap in (at which point the pressure reducer can just be replaced with a simple non return valve).  

 

In the meantime, putting the TMV where the pressures of hot and cold will be the same (beyond the reducer) seems to be the way to go.

 

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