Comparative heights of primary and cold water storage cisterns

Ric2013 · Jan 1, 2017

I have a job coming up in a house where the primary F&E is in the loft and has a tap pouring into the top of it (!) and also a combined feed and vent in 15mm. Am planning to fit FOV, add a 22mm vent, and an overflow.

My concern is that the combined cold water storage and indirect-cylinder feed cistern is on the ground floor and therefore at a lower height (pressure) than the primary cistern.

I have advised the customer that it would be a good idea to move the latter cistern into the loft to prevent contamination of the stored water in the event of cylinder coil failure. Customer likes idea and keen to get better water pressure, but reluctant to have upheaval at present - wants to rent house out.

I can't find anything in the Water Regulations that specifically says that the water level in the F&E should be higher than that in the Cold Water Storage (and cylinder feed) Cistern, but may be I'm not looking in the right place. I've said I'll do just the F&E... reluctantly - IF there isn't a regulation on this.

Is having the F&E water level lower a regulation, or just good practice? Many thanks if anyone can help!

R

chris watkins · Jan 8, 2017

Hi Ric
This may be a little late but as far as I am aware there is nothing that states that the F&E cistern water level must be below that of the secondary feed cistern. It is a recommendation just incase as you say the coil splits.

If you think about it we still have Primatic cylinders out there & pressurised heating systems with open vented hot & cold, so the potential for primary water to enter is still there but it would be cause of a failure which is a rare event.

I would certainly go with the auto fill (FOV) if it is going to be let & min size for combi feed & vent is 22mm but can't you leave the 15mm as cold feed & run the new 22mm as SOV pipe ?

Ric2013 · Jan 8, 2017

Hi Chris,

My concern was that pressurised systems only leak a bit before they lose pressure and people have to top up pressure - at least this gives some warning, but thanks, as you say, I'll take on the job.

I'll be leaving the old 15mm combined feed and vent (if it isn't blocked) as the new feed (this was already contrary to the MI from when the boiler was fitted in the late 80s), and add a 22mm as an open vent, as you say.

Apparently the primary pipework occasionally starts banging from the boiler. I suspect the boiler is kettling slightly and the pipework is not laid to a slight rise all the way to the vent and that this is causing problems. Unfortunately the pipework is boxed in, but the customer is happy to proceed on the basis that there is some additional investigation work required, so all should be well.

Thanks again.

Ric