Low Pressure HWC replacement with Mains pressure

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tritscher

3 posts

Wannabe Geek

#315091 12-Jun-2024 17:28

Hi,

Currently in a rental and the old low pressure hot water cylinder sprung a leak and has been replaced with a mains pressure. I was thinking great, now the hot water temp will match the cold and the shower will be easier to control. The issue is that the pressure reducing valve and cold expansion valve have been left on the inlet so its just the same pressure as before.

I was wondering if I can simply up the pressure on the PRV or will this just spew water out of the cold expansion valve? The hot water pipework is copper so would assume they can handle increased pressure and its currently mixed pressure so the fittings should be sweet too.

Cheers,

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#3248131 12-Jun-2024 17:46

is it the original pressure reducing valve? mains pressure cylinders still require a pressure reducing valve as a safety feature. ie so make sure cold water pressure doesn't go to high and spit the tank.

lxsw20

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#3248140 12-Jun-2024 17:55

Did they just replace the tank? If all the old valve work is still in place (low pressure), then nothing will have changed.

I have tank that will work with 7.2m head, but I just have a header tank....

Bung

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#3248142 12-Jun-2024 17:59

Maybe a photo is needed. A pressure reducing valve isn't used on mains pressure tanks, they have pressure limiting valves.

mentalinc

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#3248145 12-Jun-2024 18:06

If all the other fittings in the hours are low pressure only, they are unlikley to be able to handle the increased pressure so plumber left it running as a low pressure system maybe?

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#3248183 12-Jun-2024 20:27

There is no reason a plumber can’t install a new mains pressure cylinder as a low pressure cylinder. Doing it like that would have saved your landlord the money needed for the new valves making the install cheaper for him. There is really no difference in price between a low and mains pressure cylinder anymore.

Saor Alba

tweake

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#3248200 12-Jun-2024 20:37

my new tank came with the valves. theres no reason not to swap them over. you would have to have some really dubious pipes for them not to handle mains pressure.

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tritscher

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Wannabe Geek

#3248210 12-Jun-2024 21:38

Yea they just replaced the HWC and left all the original pressure reducing valves.

New HWC

HWC inlet valves

lxsw20

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#3248213 12-Jun-2024 22:01

Yeap thats a low pressure valve setup. That green tag will probably say you're head pressure, I'd guess 3.7m.

Jase2985

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#3248227 13-Jun-2024 05:02

tweake:

my new tank came with the valves. theres no reason not to swap them over. you would have to have some really dubious pipes for them not to handle mains pressure.

Are you forgetting about all the taps shower heads etc with would likely be low pressure only throughout the house. that matters and would be an additional cost to replace at the same time.

Dynamic

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#3248228 13-Jun-2024 05:31

Jase2985:

tweake:

my new tank came with the valves. theres no reason not to swap them over. you would have to have some really dubious pipes for them not to handle mains pressure.

Are you forgetting about all the taps shower heads etc with would likely be low pressure only throughout the house. that matters and would be an additional cost to replace at the same time.

Not wanting to hijack OP's post, but they may have a similar question in mind to me.

We've got a low pressure cylinder and our hot water flow in the bathroom is just over 4L per minute (IIRC). The shower is the most underwhelming that I've come across in a very long time, and I've tried two low flow shower heads without any notable difference in how it feels or how close to the wall you need to stand to get wet. It takes 1 minute and 10 seconds for the shower to warm up when turned on. The AJAX (?) valve is at it's limit, so turning the thumb screw only reduces the pressure.

We'd like to replace the low pressure cylinder with a mains pressure one, while avoiding replacing shower mixers for the moment. Does anyone have experience with this sort of replacement while using a flow restrictor of some sort? If we could get the shower to even 6L per minute would make a big difference, I suspect.

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Bung

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#3248230 13-Jun-2024 06:55

Dynamic:
We've got a low pressure cylinder and our hot water flow in the bathroom is just over 4L per minute (IIRC). The shower is the most underwhelming that I've come across in a very long time, and I've tried two low flow shower heads without any notable difference in how it feels or how close to the wall you need to stand to get wet. It takes 1 minute and 10 seconds for the shower to warm up when turned on. The AJAX (?) valve is at it's limit, so turning the thumb screw only reduces the pressure.

We'd like to replace the low pressure cylinder with a mains pressure one, while avoiding replacing shower mixers for the moment. Does anyone have experience with this sort of replacement while using a flow restrictor of some sort? If we could get the shower to even 6L per minute would make a big difference, I suspect.

Do you have any ordinary taps? What's the hot flow/minute from them. What's cold flow like? There may be a filter in the supply line that is blocked.

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#3248232 13-Jun-2024 07:24

Bung:

Do you have any ordinary taps? What's the hot flow/minute from them. What's cold flow like? There may be a filter in the supply line that is blocked.

I'm confident the supply into the house is fine. Cold pressure at the kitchen sink mixer, the backroom sink tap, and the laundry is amazing. Hot pressure in those same locations is very low. I'll measure it tonight.

Cold pressure in the shower is better than the hot pressure, but not by a big margin. I suspect there is a pressure limiter near the shower mixer so the cold does not overwhelm the hot.

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Bung

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#3248234 13-Jun-2024 07:38

Our last house had a "filter stop" as the tap before the Ajax valve. That had a mesh filter that could block with rust flakes. If your Ajax valve is screwed to max I'm just looking for possible flow restrictions. If your shower has a flex hose is there a big difference in flow from mixer with and without hose?

tritscher

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Wannabe Geek

#3248248 13-Jun-2024 08:56

lxsw20:

Yeap thats a low pressure valve setup. That green tag will probably say you're head pressure, I'd guess 3.7m.

Given the tank is a mains pressure can I just increase the pressure a little on the reducing valve?

Currently the hot water is completely overwhelmed by the cold water in the shower so would be nice for it to be slightly more balanced. All the other tapware in the house has mains pressure cold water so pretty sure they would all be able to handle an increase in the hotwater pressure.

WWHB

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#3248249 13-Jun-2024 09:09

Is this a Hawkes bay install, we have areas where you can no longer use copper hot water cylinders. The mains pressure cylinder may have been the closest in size to the original for changing the cylinder over as well.

Most tap ware can handle either mains or low pressure water systems, if you think about it all your cold will currently be mains pressure just now. The risk is the shower which can have a flow restrictor installed.

I am a plumber myself and the biggest risk when going from low to mains is Dux Qest pipework in the system. If you had a topliss shower mixer this would use excessive amounts of hot water after an upgrade like this so in this case I would install a flow restrictor on the shower until that was due a upgrade or replacement. Tap ware is usually rated to at least 500kPa and a mains pressure cylinder is limited to 500kPa.

Saor Alba

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