Indirect cylinder plumbing

[bigjona]

Hi there! (1st post),

I currently have an indirect cylinder which looks like it has been bodged in. It is currently
plumbed as follows:


There is some sort of very old physical thermostat plugged into the bottom of
the primary coil.

The feed goes into this thermostat.

The return comes out of the top of the primary coil.

There is link between the feed and return which has a gate valve.

Now, I am postulating that the original design was for the thermostat to block off the supply
of hot water from the boiler when a certain temperature was reached. I think the gate
valve is there to act as a differential bypass. Does this sound reasonable?

Now, I want to replace this with a new cylinder with a surface mounted cylinder
thermostat. I want this thermostat to switch a control valve which stops the feed into
the primary coil and diverts it back into the return. Now, the ways I though of doing
this are:

1) Use a proper 3 way diverter valve.
2) Use a twin port zone valve with and automatic bypass valve such that when the
zone valve closes, blocking off the feed to the primary coil, the bypass valve will
open

Does it have to be a proper 3 way diverter (i.e. can I use a 3 port mid-position valve
as they are cheaper)?

Or do I just sound mad?

Thanks for any advice!

Jon

 

[D_Hailsham]

I want this thermostat to switch a control valve which stops the feed into the primary coil and diverts it back into the return

Why do you want to do that?


Take a look at:

http://content.honeywell.com/uk/homes/systems.htm#S Plan

There are two options open to you: The Y plan, which uses a mid-position valve; or the S plan which uses two two-port valves.

It's up to you which you prefer!

 

[bigjona]

Thanks a lot for the reply. The problem I am trying to solve is the water in the cylinder
getting too hot (I am fitting a pumped shower which has a thermal limit to avoid
cavitation).

The cylinder is in the airing cupboard and has no connections back to the pump, wall
control unit or motorized valve. There is no possibility of making these connections.

The boiler currently has an arrangement where we can have the
HW or HW+CH. This is achieved with a mid position valve which, when the CH is on, is
switched to allow water to enter the radiator circuit.

So, I need to know how I can get better temperature control of the hot water whilst just
the HW is on. In this case the radiator circuit is closed so the only way water can flow
from the boiler is through the cylinder and back. If I block the water flow through the
cylinder then it needs to go somewhere doesn't it? - hence the bypass idea back to the return.

Any ideas?

Thanks,

Jon

 

[bigjona]

I should add, what I currently have is more like the S-PLAN on that linked
page.

i.e.

If boiler is on HW is always on.
If CH on timer is on, valve is actuated and water is allowed into the radiator circuit.

Basically, I want to use a cylinder thermostat to block the feed into the primary coil
of the cylinder. I am not sure how to do this (and what is safe) when the radiator circuit
is closed. With the radiator circuit it should be fine, all the hot water from the boiler will
just flow around the radiators.

So, can I do this with a diverter valve or a two port zone and a auto bypass?

Thanks,

Jon

 

[Terrywookfit]

From your description of the system you have a "Cytrol" type valve in the primary return to regulate H/W temperature!!
AS you suspect the gate valve is there as a bypass !!
This type of system was often installed as a cheap fully pumped system!!
It was even used by Grittish Bas!
The pump runs constantly during any on period of heating or water!!

Change it to an"S" or "Y" plan!!

 

[Softus]

mistaken post - please delete

 

[bigjona]

From your description of the system you have a "Cytrol" type valve in the primary return to regulate H/W temperature!!
AS you suspect the gate valve is there as a bypass !!
This type of system was often installed as a cheap fully pumped system!!
It was even used by Grittish Bas!
The pump runs constantly during any on period of heating or water!!

Change it to an"S" or "Y" plan!!

Thanks for the reply.
With the setup I have, I don't think that's possible without spending a lot of money. There is
no easy way to get connections back to the pump or 3WMPV from the cylinder. So,
essentially, I am stuck with the setup I have. The main problem being how to deal with
the feed and return when the radiator circuit is closed and the cylinder thermostat has
blocked off the primary coil. Given my situation, can I use the methods I proposed in my
first post and, if so, which one is most suitable.

Thanks,

Jon

 

[D_Hailsham]

It might be worth your time reading the Domestic Heating Compliance Guide at:

http://www.planningportal.gov.uk/uploads/br/BR_PDF_PTL_DOMHEAT.pdf

My reading of this is that, if you replace your HW cylinder, you will have to make the system comply with the regs and have proper control over the pump and boiler when the HW cylinder is not calling for heat.

If you are thinking of putting a motorized valve and thermostat in the airing cupboard with the new cylinder, you can presumably get an electrical supply there. Is there no way of running cables back to where the rest of the installation is situated?

Just for info, what boiler do you have?

A quick sketch (use Paint and save as a jpg) showing where the components are located might help to suggest a solution.