Is it OK to use a part 4 fill valve in a cold water storage cistern?

[MickBee]

The old (40 years+) ball valve in the cold water cistern in our loft needs replacing - a slight leak to the overflow. I had intended to do it but a health problem means that I have been asking plumbers for quotes for a non-urgent repair, mentioning the replacement fill valve a Fluidmaster PRO75B] that I have bought.

One plumber has replied "You cannot put the fluidmaster on there." and when I asked why, wrote "Water regs do not allow you to fit a part 4 fill valve to a cold water storage cistern. The Fluidmaster PRO75B is a part 4 valve. You have to fit a part 2 valve."

On the box of the Fluidmaster is written "For use in a toilet cistern or storage tank" and "Anti-syphon prevents contamination"; none of the websites that I have seen suggest that it is unsuitable. Is the plumber mistaken (and/or drumming up trade) in suggesting that I should "book in to supply and fit a part 2 fill valve"?

I'm attaching some photos, one of which shows that the inlet is well above the overflow outlet, so there should not be a backflow risk. (n.b. the shiny screw in the close-up has temporarily replaced a copper split-pin that disintegrated when I tried to remove it.)

[I know that cheaper valves are available, but chose the Fluidmaster as it has a brass connection and seemed easier to service and more reliable than some. I don't want to return it to my local merchant if it is suitable, which is the question that I'm asking.]

 

[denso13]

The Fluidmaster has a WRAS type AG air gap approval which is not suitable for a storage cistern. It needs to be type AA so go with the plumber's advice.

 

[MickBee]

Thank you for your quick reply, and advice which I'll take.

My delay in responding was because it raised questions which others might have, if not getting professional help:-

1) How does one find the air gap approval type (AA or AG)? I can't see it on the Fluidmaster (or any other) website.

2) Why is the water in a storage cistern for domestic hot water supply categorised as Fluid Category 5 according to https://tricelwater.co.uk/compliance/backflow-prevention-in-building-water-systems/ when the government website https://www.legislation.gov.uk/uksi/1999/1148/schedule/1 describes Fluid category 2 as Water in fluid category 1 whose aesthetic quality is impaired owing to – (a) a change in its temperature, or (b) the presence of substances or organisms causing a change in its taste, odour or appearance, including water in a hot water distribution system. [my underlining] and Table 1 allows type AG as suitable for fluid categories up to 3? [n.b. the Tricel website (2026 update) then has "A cold water storage cistern is classified as Fluid Category 5 under the Water Fittings Regulations, requiring a Type AG or Type AA air gap at the inlet."]!

3) Are "part 4" and "part 2" (as used by the plumber I quoted) obsolete terms for fill valves?

 

[denso13]

3) Are "part 4" and "part 2" (as used by the plumber I quoted) obsolete terms for fill valves?

Not really, just a different terminology. The "parts" refer to the different 4 parts of BS1212 for float valves. You'll see, for example, part 4 covers valves for use in toilet cisterns.

2) Why is the water in a storage cistern for domestic hot water supply categorised as Fluid Category 5

Because it's uncontrolled storage and can be used as drinking water. I've removed many a rotten pigeon/starling from storage cisterns, not nice.

1) How does one find the air gap approval type (AA or AG)? I can't see it on the Fluidmaster (or any other) website.

The only WRAS approval for anything to do with fill valves is the bottom one here, https://www.wrasapprovals.co.uk/approvals-directory/?search=fluidmaster

 

[endecotp]

I've removed many a rotten pigeon/starling from storage cisterns, not nice.

Yes, pigeons and also legionella.

 

[denso13]

Yes, pigeons and also legionella.

That's more on hot water parts, but yes, plenty of contamination routes.

 

[endecotp]

I think the idea is that the legionella bacteria enter through the exposed roof tank and then multiply in the hot water cylinder. Which raises the question, do we need legionella precautions in mains-fed high-pressure hot water cylinders? Anyway, that’s all off-topic.