Unvented/G3 ongoing install sanity check

[Gasguru]

The cylinder manual will tell you exactly how it should all be installed, it really is simple...point out all the errors to this clown and insist on seeing the card.
Google the combination valve...it specifically mentions the vessel connection port, otherwise it needs teeing in between the cylinder cold inlet anx combination valve set.

Thermal stores store the water at much higher temperatures hence a blending valve to drop the temp down to 60 degrees...should not be needed on a standard unvented. Bath taps etc if protection required should have the TMV installed near the taps.
All this work is also notifiable to the council so make sure you get the certificate.

When your boiler packs up and you can switch on the immersion heater you'll be pleased to have a cylinder...make sure the elements wired up too.

 

[NoRulesRules]

Thanks for all the advice.

Its just occurred to me that there is another problem too. The balanced cold feed only goes to the vessel (incorrectly) and the TMV (not needed). The TMV then outputs a moderated hot, but where is the balanced cold going to?! I have a mixer shower that should be getting hot and balanced cold.

God what a nightmare.

I'll attempt to point out as much as possible tomorrow and then seek further validation of G3 and some sort of second pair of eyes.

 

[Gasguru]

The balanced cold carries on up past the vessel doesn't it?

 

[NoRulesRules]

The balanced cold carries on up past the vessel doesn't it?

Oh, Yes good spot, that goes to the shower supply in en-suite (via loft), the only mixer supply in the entire house.

 

[Gasguru]

But the balanced cold should ideally feed all the cold taps and that's very important if you have an incoming pressure that's considerably higher than the hot regulated pressure.

 

[NoRulesRules]

But the balanced cold should ideally feed all the cold taps and that's very important if you have an incoming pressure that's considerably higher than the hot regulated pressure.

Why is that? To account for future potential use of mixer taps that "mix in tap" as opposed to having separate channels?

 

[Gasguru]

Yes and the problems that can cause...it's feasible that you could have a mains static pressure of say 7 bar but the expansion valve is only 6 bar and therefore could discharge from back pressure via the cold.

 

[Mottie]

Sounds like a right balls up. I'd stop work until you’ve spoken to the man in charge.

 

[NoRulesRules]

Yes and the problems that can cause...it's feasible that you could have a mains static pressure of say 7 bar but the expansion valve is only 6 bar and therefore could discharge from back pressure via the cold.

Thanks good to know. Will stick to the "dual chamber" mixers to avoid this in future. Sounds like its the least of my worries at the moment.

To be fair, to pipe the balanced cold to every outlet in the house would be a nightmare plumbing job. For example the stopcock/mains feeds enters in the downstairs w/c, and the sink in their T's straight off it. How would you get a balanced there without ripping up most of the upstairs flooring.

But point taken. Appreciate your comments

 

[NoRulesRules]

Sounds like a right balls up. I'd stop work until you’ve spoken to the man in charge.

Quite painful when its 50% done and we are without hot water/heating. But I suppose you are right, with a long term view, this does not get any better if I let work continue without escalating.

 

[JimCrow]

Thanks for all the advice.

Its just occurred to me that there is another problem too. The balanced cold feed only goes to the vessel (incorrectly) and the TMV (not needed). The TMV then outputs a moderated hot, but where is the balanced cold going to?! I have a mixer shower that should be getting hot and balanced cold.

God what a nightmare.

I'll attempt to point out as much as possible tomorrow and then seek further validation of G3 and some sort of second pair of eyes.

The reason for the TMV is you are having solar heating.

 

[NoRulesRules]

The reason for the TMV is you are having solar heating.
View attachment 223146

Does not make sense for simple unvented design where solar is just being used as secondary coil for hot water. If hot water temp in the cylinder exceed 60c, the solar thermal wont heat the water beyond this. Just like a gas boiler would not.

Edit. Unless I missed anything. Sorry, wanted to add that, dont want to sound dogmatic or like I know anything/everything

 

[JimCrow]

But the balanced cold should ideally feed all the cold taps and that's very important if you have an incoming pressure that's considerably higher than the hot regulated pressure.

From Gledhill,

 

[Gasguru]

The diagram shows a balanced cold feed to all outlets fed by mixers where there is the potential for the cold to back pressure the hot so no you don't need to feed WCs etc. Check valves are shown but they are often missing or fail to work. Note the absence of a vessel.
I rarely see solar but if the temperature is too high the overheat thermostat on the cylinder will trip...what is the maximum temperature the solar controller will allow?
Have you done your maths...I've just reviewed my gas bill with my own meter readings, our annual hot water usage was only around £150. AFAIR solar is reckoned to save 50% at best, well that saving won't even cover the annual servicing and routine maintainence (vessel checks, chemicals etc).

 

[NoRulesRules]

The diagram shows a balanced cold feed to all outlets fed by mixers where there is the potential for the cold to back pressure the hot so no you don't need to feed WCs etc. Check valves are shown but they are often missing or fail to work. Note the absence of a vessel.
I rarely see solar but if the temperature is too high the overheat thermostat on the cylinder will trip...what is the maximum temperature the solar controller will allow?
Have you done your maths...I've just reviewed my gas bill with my own meter readings, our annual hot water usage was only around £150. AFAIR solar is reckoned to save 50% at best, well that saving won't even cover the annual servicing and routine maintainence (vessel checks, chemicals etc).

I think Jim's point is that you don't need to take the balanced cold to every cold tap which was the original comment. You are both right, considerations should be made for any mixer units.

After doing some further reading, I believe the reason the blend/TMV exists, is for 2 reasons in the context of solar. 1) Because of the potential for high temperatures (catering for the "what if" safety scenarios) and 2) So that you can run the hot water out feed at a higher temp (80c as opposed to 60c for example), which allows you to get more out of the Solar panels before stagnation occurs.

Regarding the financial viability of the setup, yes its no home run that's for sure. It's only made viable due to the government green grant, otherwise pay back period would be 25+ years, and as you say, increased maintenance overhead further eats in to that. However for us, the figures made sense, because we needed to replace the entire heating system anyway, and the green grant allows you to subsidise the cylinder refresh cost, which comes as part of the Solar Thermal pack. Now if I could turn back time, I would probably have not bothered with the green grant, ignored the Solar thermal, and gone with my normal guy, but you live and learn.