Convert regular s plan boiler to system without changing boiler?

[finlaand]

Hello

Have WB 40cdi, hw feed/ expansion and CW tanks in loft...regular system, shower pumps ect, indirect cylinder.

Plumber said as boiler works fine, if I want to get space in the loft, he can make it a system setup...but keep the boiler as is.

Just change to unvented indirect cylinder same place, remove feeder and cold tanks and remove shower pumps, and add expansion vessel by boiler with some pipework (prv/ drain off/ overflow ect).

That makes sense? I had thought you couldn't do that bit needed to also change the boiler but he no need

 

[Madrab]

That boiler can run as a sealed system. The system will need pressure tested properly before going from atmospheric to a sealed pressurised system to avoid any wet disasters

Do a proper check on the mains dynamic water pressure and flow though to ensure the mains is suitable to support an unvented HW cylinder adequately.

 

[finlaand]

Mains has a pressure relief valve fitted earlier this year right after the main incoming stopcock. Currently set at 50psi, as too high in winter. That help?

The flow on kitchen cold tap I tested with 5 Litre test, worked out c19.5 litres a minute.

 

[Madrab]

pressure relief valve

It'll be a pressure reducing valve (PRV), relief valves are safety devices that release over pressure when a certain level is reached but I get what you mean.

That's set to 3.5bar which will mean your pressure obviously climbs higher than that. That's a good start but a dynamic figure for flow and pressure is needed just to confirm. Does the PRV have a gauge on it? What will the unvented be supplying in terms of bathing etc?

1 way to obtain the dynamic pressure and flow figures:-

On an outside tap - fit a pressure gauge - loads available cheaply online that will fit, and open the tap, take the pressure reading with nothing running, that's the mains static pressure. Then fully open up a tap say in the kitchen and check the pressure drops taking a note of that reading, that's the working pressure > now leaving that running go to the bathroom and open up a bath or basin tap full and then check the pressure again, that's the dynamic pressure. (working and dynamic are basically the same but I use the terms slightly differently when it comes to domestic mains)
Once that's done remove the pressure gauge from the outside tap and whilst running both the sink tap and the bathroom tap, open the outside tap and fill that container timed over the minute as you had done. Then measure how much water is in the container, that's the dynamic flow test.

Ideally you are looking for at least 2bar dynamic @ a flow rate of ~20L/Min.

 

[finlaand]

This is a Segway from the query
. Which is can what the plumber suggests work, which you said yes.

Can it run two showers at once, which I looked at chatgpt there and it said yes 20l flow when you assume a 60:40 ratio hot to cold, at 55c heated water in tank, would work.

Anyway I'll try your item in a few days, basically it's two separate cold pipe runs at different points in the house to see the drop, clearly if max going in is 20l/m and three outlets open it will not be 20 out.

 

[finlaand]

Oh plumber pinged me to say both the gledhill cylinder will have expansion vessel, as well as separately the boiler have one added.

 

[Madrab]

clearly if max going in is 20l/m and three outlets open it will not be 20 out.

Unfortunately that's not quite right - if the the dynamic pressure is good enough and the flow is through large enough pipework (22mm that branches down to 15mm to the outlet) then that 20L/Min could be maintained to both but chances are the shower wouldn't need that anyway.

I have 3 showers - 2 en-suite and one main bathroom with a dynamic pressure, when all 3 are running, of 2.8 bar with a flow rate of 22L/Min. With one shower running it's 3 bar @ 25L/Min. I have a mains that runs ~@ 3.3bar dynamic with a 28L/Min flow rate (limited). All depends on the output of the showers too, as to how much flow they will draw.

It's all down to how well the system is designed as to how well it performs. The best saying with unvented is "you can only get out what you you put in" if properly designed by someone that knows what they are doing then pressure and flow can easily be maintained.

Yes and unvented will need it's own expansion unless it has it's own internal bubble