Can I isolate CH from the HW on a gravity fed hot water system?

dougalhouse · 6 Jun 2018

Would someone please advise me on whether this is possible?
My property is a bungalow with an oil fired boiler and gravity fed HW system (I think!) I have removed 2 rads from 2 bedrooms and drained the CH system down (I thought I had isolated the CH feed from the HW as there was an isolator valve coming from the loft tank but this appears to feed the boiler for the hot water too and the system doesn’t have a diverter valve). The CH pipes are buried in the concrete flooring and I am going to be putting in electric underfloor heating in the bedrooms so I cut the copper tails flush with the floor and now I’ve realised that I can’t now reinstate the hot water. So my question is how can I isolate my CH from the HW with this type of system? Thanks in advance.

gassymark · 6 Jun 2018

Hi matey goggle primatial cylinders, but your gonna have to cap the pipes . Cheers mark

gassymark · 6 Jun 2018

Not sure how to edit but supposed to say Primatic sorry.

dougalhouse · 6 Jun 2018

Thanks for the reply. So am I right in thinking that when the central heating is running it also heats the water in the cylinder? And if so how come when the HW is switched on, the CH doesn’t come on?

stem · 7 Jun 2018

Heated water will travel from the boiler to the hot water cylinder by natural circulation. [Hot water rises, cooler water falls] to allow this process, flow and return pipes directly between the two are usually around 28mm diameter and rise vertically. This natural circulation doesn't occur so readily in radiator circuits because of the smaller pipe bore, horizontal pipe runs and greater resistance to flow through the radiators, so a pump is added to circulate the water around them.

When hot water only is required the boiler is switched on and the natural circulation through the hot water cylinder occurs. [No, or little circulation occurs through the radiators]
When heating is required the boiler and pump are on and the radiators also are supplied with hot water.

Primatic cylinders are very old and quite rare these days. The clue as gassymark noticed, is that with your system as you describe it, there only a single cold water storage tank supplying both the heating system and the domestic hot water supply, instead of them having one each.

Most Primatics have been taken out during boiler replacements as new boilers need to be connected to fully pumped systems and won't work with them.

dougalhouse · 7 Jun 2018

Thanks,I have recently moved into this property and it hasn’t been updated for many years and it must be, if not the original system, then close to it. This system has a large water tank that feeds the cylinder in the airing cupboard and then there’s a small tank that drops down in 15mm then 28mm into bottom of cylinder then drops to bottom of boiler.

On the opposite side is this configuration of pipes

So how would I disconnect the CH completely for the time being so that I can just have the boiler running the HW? Could I just disconnect the T above the 90 degree elbow and cap that off til I’m ready to reinstate the CH?

Terrywookfit · 7 Jun 2018

What pipes are at other side of the oil boiler.

dougalhouse · 7 Jun 2018

dougalhouse · 7 Jun 2018

This is the other side of the boiler.

Terrywookfit · 7 Jun 2018

just disconnect the pipes at the right hand side of boiler and put a BI plug in the tappings .
Boiler will work on gravity H/w

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Can I isolate CH from the HW on a gravity fed hot water system?

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