Draining Cold Water Tank To Replace Taps

Hiya, what started as a simple job seems to have become complicated. My friend lives in a small flat and has a pressurised cold water system that feeds a wall mounted boiler. I believe it is a "megflow" system? I intend to replace all her taps, 2 basin and bath taps in the bathroom and 2 taps and sink in the kitchen.

The kitchen taps have service valves but one of them is seized so I couldn't isolate those taps. The bathroom seems to have no isolation / service valves at all so it seems I will have to drain the cold water tank to stop the flow of how water, and find a stopcock to stop the flow of cold.

My plan was to stop the main cold water supply into her flat from the main valve in the lobby downstairs (there appears to be one for each flat) then make sure the boiler is powered off, then run the taps until no water flows (although I understand this can be quite a long process in terms of the hot system) then cut the pipes for each tap and fit a plastic service valve to each (before attaching new taps to pipes and conecting them. What I am not sure about is refilling the system. If I simply restart the cold supply again I assume the tank will just refill to its own level and then stop? Also it has a separate gate valve that controls the pressure within the system. Do I just need to make sure that once the tank is filled, that this is at the correct setting?

Am I ok so far, or am I completely wrong!!!??? I think the system is Heatre Sadia or similar...

Mart864 said:

...it seems I will have to drain the cold water tank to stop the flow of how water, and find a stopcock to stop the flow of cold.

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If you have a Megaflow providing hot water at mains pressure, then there no cistern to drain. Confirm this by shutting off the cold main and opening a hot tap - very little water will come out.

What I am not sure about is refilling the system. If I simply restart the cold supply again I assume the tank will just refill to its own level and then stop?

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Yes, but even more quickly if there's no tank/cistern to fill.

Also it has a separate gate valve that controls the pressure within the system.

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Eh?

Also it has a separate gate valve that controls the pressure within the system. Do I just need to make sure that once the tank is filled, that this is at the correct setting?

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I wouldn't touch it.

If it is a megaflo then there will be an isolating tap built into the pressure reducing valve, the big black thing near the megaflo. This will turn off all hot taps and balanced cold taps.

If in doubt turn off mains stop cock and run all taps until water stops running out of taps.

When refilling make sure you leave one hot tap open. This allows the megaflo to vent during filling.

Thanks for your replies...

Sorry I didn't describe the system very well.. My terminology may be highly suspect. It does say Heatrae Sadia (or similar) on the tank.

I will try the closing the mains tap and running the hot water to see. I suspect though the tank will empty first.

Im assuming this is an "unvented" "indirect" heating system as there is a closet room fitted with a large white plastic tank full of cold water. A 22mm mains pipe comes along the bottom of the closet straight through to supply the cold taps in the bathroom and I guess through to the kitchen. A smaller 15mm pipe links this to a device attached to the cold water tank. Something (I assume the tank) is pressurised and there is a guage showing the presssure with a gate valve attached to it. My friend was instructed to open this valve and get the needle to a given setting to maintain pressure, every now and then. Being a flat there is no gravity feed so I guessed that this tank feeds the Potterton Prima condensing boiler. Two pipes exit the top of the boiler and I assume one feeds hot water taps and the other feeds the radiators for central heating.

I think the last bit of advice seems sensible. Open a hot tap and refill.. I hope these push on connectors are as good as I hear... I just wasn't sure how to refill this tank, the gate valve with the guage definately allows water to flow under pressure as you can hear it.

I just can't find any valves to isolate the taps from the water supply and wondered how to do this. My house has plastic service valves all over the place and it makes this sort of job straightforward!