Re: Automatic water pressure maintainer for combi boiler system?



Well, on my own combi-fed central heating system, I have to keep checking the pressure occasionally by looking at a dial on the front of the combi. Every time the pressure drops below the recommended minimum, you have to manually top up the pressure using a removeable link to the mains water supply. What I'm thinking of is a device that will keep doing that for you whenever the pressure drops (say due to small leakage at pipe joins or whatever). My own system often needs its pressure topping up manually.
Frank
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wrote:

It has to be topped up manually. If it keeps dropping you have a problem, such as: water leak, the pressure in the pressure vessel needs topping up, the diaphragm in the pressure vessel is holed, hole in the plate heat-exchanger, etc.
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wrote:

Andy - That's all very helpful advice; thank you! I will certainly follow your suggestions.
BTW, re the water-pressure maintaining device... seems like a good project for an inventor with plumbing knowledge. I suspect there may be an alternative solution to the one you saw with the header tank and electric pump. If anyone knows of one - or invents one, that is cheap and effective, please post a description of it here...
Frank
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The system IS NOT supposed to be permanently connected to the mains.
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IMM wrote:

A simple implementation (which would fall foul of several bylaws) would be a pressure reducing valve, set to 1 Bar output and then a filling loop permanently connected and opened to the heating circuit. This would ensure the circuit never fell more than a small amount below the 1 bar from the reducing valve. When the system is hot the NRVs in the filling loop will keep it in.
Unfortunately a failure mode of PRVs is to let full pressure through, which would be a bad thing.
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NEVER disclose a new idea here or elsewhere in public before the patent is filled or you will lose all patent rights!!!!!!!!!!
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Frank W wrote:

Very bad idea. If you've got a leak it should be fixed 1) you don't know where the water is going and rotting it may cause. 2) constantly changing the water in the sealed system will hasten its demise due to corrosion.
Small leaks that cause you to top your system say once a month can be cured with the Fernox stuff in a standard cartridge that can be injected into radiator bleed valve. Has worked 100% for me on 2 different systems. Mind you its not cheap RRP >20 I found mine on special offer at a plumbers merchant.
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BillR wrote:

It does depend on how often he is topping up. It might be going a couple of months between top ups but the OP really hates doing the job. ON the other hand there may be a big leak (or other problem) whcih needs fixing pronto.
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If you rent it out you need a CORGI landlords certificate. He will fail the combi. Get it fixed.
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I wasn't aware of that. Thanks for pointing it out.
Frank
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I recently did some work to my system (replaced two radiators, and one TRV). I too suffer from regular topping up. I suspect this is from small leaks at the BSP tails and/or the pipe/valve joints. If the leaks are small enough then the water evaporates from the heat before you notice it.
Anyway, the interesting thing I found was that the system holds approx 50 litres of water, yet it only takes loss of 1 litre to cause the pressure gauge to drop from 1 to almost zero (on a 7 rad system with a really old Valliant combi).
I used to get concerned when the gauge dropped this low, but not anymore.
If you have a leaking BSP tail / rad joint then it can be re-taped (PTFE) without draining the system. Just shut off the rad valves, and put a towel down to catch the leakage. Use a BSP plug to cap off the rad while you are re-doing the PTFE tape. I did this last week for two new radiators, and only lost 0.5 litres per radiator.
Ian

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"I.Wilson" wrote:

Replying to top posted reply :-(.
Check the operation of the expansion vessel and/or drop its pre-charge pressure to about 0.6 bar.
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A header tank, surely? ;-)
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Andrew Gabriel

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