Boiling hot water in the hot press cylinder- Any advice on thermostatic mixing valve?

monica555 · 31-03-2014 03:13PM #1

Hi there,

I have enough washing my hands under cold water, at the same time when the immersion tank is full of hot water, just to avoid scalding.
I am thinking about installing a thermostatic mixing valve on the out of the immersion cylinder so that it would serve the entire house.
Please, let me know if you have any good or bad experience with this kind of valves and if you can recommend a particular brand or model available either in Dublin area or on the Internet.
How long would it last in the case of a water softener being installed?
Also, I wonder if such a valve would be a bottle neck of my open system where the storage tank on the attic is only about 3 meters above the taps in the bathroom.

I know there is number of other possible solutions to my problem but it seems neither of them is perfect.
With mixing taps there is still risk of scalding, I see my young kids being most vulnerable here. But also, the temperature may change suddenly when someone opens another tap somewhere in the house and this might be particularly unpleasant when taking shower.
A thermostat attached to the immersion cylinder set to say 41 degrees Celsius, controlling an electric valve on the hot water coming to the cylinder from the gas boiler would do the job. However, this lower temperature in the cylinder means running out of hot water very quickly and having to turn on and off the gas boiler more often. Also, the cylinder would be a perfect ground for legionella (I am not entirely sure how serious it is).
Any advice welcome!!!

shane 007 · 31-03-2014 05:03PM

Best ones are Esbe.
What distance do you have from the level of water in the cwst to the outlet of the cylinder?
The pressure at this point is important as the valve will use up approx 0.1bar of pressure to open. So if you have 3m at the bathroom tap, this is 0.3bar pressure. With the valve, you will now have 0.2bar so 1/3 less pressure.
Downstairs outlets won't notice that much of a difference.

antoinolachtnai · 31-03-2014 07:05PM

How hot is the water coming out of the tap?

Have you tried reducing the temperature of the central heating circulating water (i.e., the temperature on the boiler)?

This might solve your problem. If it is a condensing boiler, running it at a lower temperature will make it more efficient.

I would not worry about having to turn the gas boiler on more often to top up the hot water. This doesn't make the system less efficient. In fact, it will be more efficient, because if the cylinder is at a lower temperature, it will lose heat at a lower rate.

You might find you have to run the boiler for longer to get the same amount of heat in the house at the lower temperature, but as I say, it will be more efficient.

If you introduce something like the mixer valve, you are making your plumbing that bit more complex and unusual. This might not be a problem in the short term, but if at some stage in the future you have a problem, and need to get it serviced, that could make the diagnosis and repair a lot more complicated and time-consuming.

In relation to legionella, I suppose you have a copper tank. According to the Copper Tank Lobby (there is such a thing, believe it or not) these tanks are naturally antiseptic. See for example http://mcdonald-engineers.com/blog/index.php/how-to-prevent-legionella-in-hot-water-cylinders/ . I cannot tell you how much you can rely on this. You would need an experienced plumber to tell you the current view on the Irish situation. (I am just a householder with a good bit of experience with plumbing stuff.) It is also worth reading http://www.plumbingengineer.com/march_13/code.php which has all the charts. Also, http://www.seai.ie/EnergyMAP/Identify/Step_7_Identify_key_factors_that_influence_energy_consumption/Step_7_Guide_1_Energy_Survey_Checklist/ recommends a temperature of 55-60 degrees C.

My own experience (no kids in the house, so not too worried about scalding risk) is that I have the water in the tank quite hot (boiler runs at 65C when it is heating water) and that the temperature falls off by the time it reaches the bathroom taps (which are about 5 meters away from the tank, and the piping is 1/2 inch plastic piping).

monica555 · 03-04-2014 07:27AM

Hi Shane 007,

Yes, both the cylinder outlet and the shower are more or less at the same level and around 3 meters below the level of water in the cold water storage tank.
Is 0.2 bar enough for shower, do you know?

Thanks for ESBE. They have a nice website with all the tech data, installation guides, etc.

monica555 · 03-04-2014 07:40AM

Hi antoinolachtnai,

Thanks for all information. My husband will try that.
We have a gas heating. The whole system is very old so we don't have much control over the temperature.
Yes, we have an old copper tank. It's not insulated and at some stage was leaking:( We have a plan to update the whole system in the next few weeks, getting new cylinder and cleaning the attic tank. We are also thinking about getting a water softener system. Our kids have problems with their skin and our GP said it might be something to do with very hard water. Limescale everywhere:(

antoinolachtnai · 07-04-2014 11:55AM

That is great. You are better getting the best 'core' heating system you can rather than putting on things like mixing valves. They seem like small items but the cost adds up.

I have a Viessmann boiler. It is plumbed in the 4-pipe configuration, which means that I can control the hot water and central heating temperatures separately.

Boiling hot water in the hot press cylinder- Any advice on thermostatic mixing valve?

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