Indirect Unvented cylinder, Combi Boiler and Nest Thermostat

[Chris1012]

We have just had an indirect unvented cylinder (250l Vertical Telford Tempest) installed along with a nest v3 thermostat.
The plumber was able to modify our existing combi boiler, so it runs like a system boiler.

I am trying to understand how it works as currently the plumber has set it to come on for 2 hours each day (1hour between 5am-6am and 5pm-6pm).
During these times, the boiler remains continuously on and only switches off after the hour mark.
Is this right?
I would have thought during the set times that the boiler should come on, it would work in connection with the cylinders thermostat so once the waters heat got to a set level, the boiler will shut off.

The cylinders booklet states it takes 28min for it to heat up.

Could someone please advise on how this setup should be working and if there is anything I could do to make it more efficient, then it currently is?

Thank you

 

[Welder]

We are at cross purposes.

The outlets do indeed draw their water from the cylinder. As the stored HW is used then temperatures at the outlets reduce.

What I was talking about was the time taken for the temps to recover (go back up). Most manufacturers give an indication of the time taken to heat a cylinder of cold water to approx 60 degs C. To understand whether this is realistic (indicative of the world we inhabit not the one manufacturers inhabit) we need to know the temp of the water going in (the lower the temp (say winter) the longer the recovery time, and the temp of the heating water through the coil. Most heating coils operate at approx 70 deg C buit the one I was referring to said it assumed a heating coil temp of 80 degs C. Frankly its unrealistic.

Bottom line. Take ALL numbers issued by manufacturers with a BUCKET of salt. YOUR circumstances dictate what will happen as every installation is different.

HTH

 

[AWheating]

The cylinder will only heat up at the time in the instructions in ideal conditions. Unlikely in real world situations. Time the hot water to be on without the heating so it's coil gets the boilers full output and it won't take too long. Have the heating on and it will get a share of the boilers output. Best to set hot water to come on one hour before heating times.

 

[AWheating]

a combi with an unvented cylinder is fine, all manufacturers will happily agree to this. Most manufacturers will have a drawing showing there boilers with cylinders. They won't show the full technical spec of an unvented cylinder of course as that's down to the cylinders manufacturer to spec.

 

[Chris1012]

The cylinder will only heat up at the time in the instructions in ideal conditions. Unlikely in real world situations. Time the hot water to be on without the heating so it's coil gets the boilers full output and it won't take too long. Have the heating on and it will get a share of the boilers output. Best to set hot water to come on one hour before heating times.

During last weeks heat wave, I was testing the hot water at each outlet. As the weather has been pretty mild since last week, the heating has not been on at all.
When I am testing the hot water at each tap, no other service is in use, including rads or UFH.
However it seems to still be the same heat up time from last week until today - average of 40seconds to get hot water!

 

[Welder]

Ahh. Is what you are talking about is the time for the hot water to reach the taps? If it is there is nothing you can do without massive investment. This would be the same issue regardless of whether an Unvented cylinder or combi is installed in the same place. It is a product of the distance the water has to travel and an UVC cannot, for obvious reasons, be located as closely as say a combi can in a kitchen.

 

[Gasinspect]

We now fit a circulating pump on the hot water from the cylinder. Combi heats it fine, all hot water taps from cylinder so no time lag. Put circulator on a ceiling mounted proximity sensor so that runs for 15 minutes when activity in the bathroom area. The kitchen sink near enough not to need circulation.

 

[ShaunCorbs]

We now fit a circulating pump on the hot water from the cylinder. Combi heats it fine, all hot water taps from cylinder so no time lag. Put circulator on a ceiling mounted proximity sensor so that runs for 15 minutes when activity in the bathroom area. The kitchen sink near enough not to need circulation.

You mean a src (secondary return circuit)

 

[Welder]

Im assuming that too Shaun. Fact is tho that is not always an option. Plus, in its life, it wastes huge amounts of energy if its a retrofit because no pipework will be insulated. Frankly its cheaper to waste water.

 

[dan_the_plumber]

Combi on unvented is fine. If you’ve got your 2 port valve and all other G3 kit installed correctly then there nothing wrong with that at all. Assuming it’s installed correctly the coil is just like another radiator

 

[Harvest Fields]

Combi on unvented is fine. If you’ve got your 2 port valve and all other G3 kit installed correctly then there nothing wrong with that at all. Assuming it’s installed correctly the coil is just like another radiator

That’s also what we were saying mate