Improvements for pre-lagged DHW cylinder

Teka · Jun 23, 2023

I have a factory lagged indirect hot water cylinder in the airing cupboard, installed about 2002. The control thermostat is fitted near the bottom of the cylinder and the primary circuit connections are near the top and bottom of cylinder connected to a gas fired boiler. This results in nearly a full cylinder of hot water before the stat switches off

I do not need all this heated water

Are there any easy alterations I can make to save the cost of this unwanted hot water?

All suggestions appreciated

fowlerboi · Jun 23, 2023

in your programmer set the time the hot water runs for for less
Maybe 20 mins a day?

You’ll need to do a weekly heat up of the entire cylinder though to prevent legionnaires

Basher · Jun 23, 2023

If your thermostat is the type strapped to the side of the tank (having removed insulation), rather than in a pocket, you could move the thermostat up the tank. But this would mean never having a full tank of hot, which might be a problem!

John.g · Jun 23, 2023

Some coils only have a dT of 8 to 10C or less as they don't have a balancing valve (nor is it now recommended) so the above (moving the stat up) would help, if the balancing valve is already installed, then by throttling the flow to get a dT of say 20C should result in a much reduced effective HW capacity.

SimonG · Jun 23, 2023

How much hot water do you need and where?
I've seen small houses, flats and apartments with a cylinder, no bath, electric shower and the cylinder just providing to basin and kitchen sink. Stripped out cylinder and fitted a 15 litre hyco under sink unit to do sink and basin.

Teka · Jun 25, 2023

I want hot water for2 x 4 minute showers

I don't know how the thermosat

is attached to tank so I have added photo

John.g · Jun 25, 2023

There may be a dry pocket with the thermostat but then there shouldn't be a need for the insulation cut out which is normally done for a contact type stat with a external spring holding it in contact with the cylinder wall. Its hardly likely that someone installed the stat and spring before spraying on the insulation!!, just pull it out carefully, if its a rod type then can't be used further up, a contact type would need to be purchased and some insulation removed.

Basher · Jun 25, 2023

I'd be inclined to leave that stat as is (in case you need to revert), and buy another equivalent to fit higher up, cutting the foam insulation out as necessary. Then wire in it place of the previous one (or you could connect them both in series, and choose which will turn off the boiler by twiddling the temperature knobs appropriately!)
ie top stat set to 65, bottom one to 90, half a tank of hot. Other way round, full tank!
e.g:

https://www.NoLinkingToThis/p/floma...0v/6803k#product_additional_details_container

snowhead · Jun 25, 2023

It's one of these below.
It would normally have a plastic coated spring (net curtain wire, pictured in blue) over the front and around the tank to hold it in place, but looks like someone has just cut the foam off so the stat fits in tight.

John.g · Jun 26, 2023

It will be interesting to see what effect positioning a stat higher up will have with no throttling of the coil flow, the stat is normally positioned maybe a 1/4 way up the coil, this means the cylinder will start reheating after a small amount of HW is drawn off, the higher the stats positioning means more HW has to be drawn off before reheating, the whole cylinder will still reheat but probably with a bigger temperature gradient?.

SimonG · Jun 26, 2023

John.g said:
It will be interesting to see what effect positioning a stat higher up will have with no throttling of the coil flow, the stat is normally positioned maybe a 1/4 way up the coil, this means the cylinder will start reheating after a small amount of HW is drawn off, the higher the stats positioning means more HW has to be drawn off before reheating, the whole cylinder will still reheat but probably with a bigger temperature gradient?.

Depends on time control as well. I used to run ours an hour in the morning and an hour at night.

Teka · Jun 26, 2023

Thanks everybody for your help

I have taken the plunge, pulled on the stat and found that it is just sitting in a hole cut in the insulation, so I should be able easily reposition it nearer the top

gmartine · Jun 27, 2023

Fit an insulation jacket on top of existing.

John.g · Jun 27, 2023

Try and get a spring to hold the stat right up against the cylinder wall.

gmartine · Jun 27, 2023

Yes, usually just net curtain wire.

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Improvements for pre-lagged DHW cylinder

Teka

fowlerboi

Basher

John.g

SimonG

Teka

John.g

Basher

snowhead

John.g

SimonG

Teka

gmartine

John.g

gmartine

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