How to work out my central heating layout

[andrew45]

Hi there,

I have just bought a house and the central heating system is fully pumped but has an old electromechanical timeswitch that allows CH + HW or just HW.

I'd like to modify the system to allow completely independent CH & HW control but need to understand the layout of the existing system to know whether it is suitable or what needs changing.

Can anybody possibly advise on the best way to discover the plumbing layout of an existing system, e.g. how to trace pipes from the boiler to the airing cupboard when they disappear into walls/floors and then pop out somewhere else!?

I guess I need to reverse engineer the system to understand what I have and I'm looking for tips on how to best do this.

Any help much appreciated.
Thanks,
Andrew

 

[seco services]

can you have ch without hw ?

 

[andrew45]

Nope, that is what I want to achieve. At the moment I can have:
CH + HW
OR
HW only

I would like:
CH + HW
OR
HW only
OR
CH only

Regards
Andrew

 

[East Kent Coastal]

Assuming that you have a pretty standard conventional system layout, it's more the controls (motorized valves, programmer/timer) and associated electrics that you want to be looking at.

(There are variations on a theme but...) The primary flow from the boiler should come up in the airing cupboard to a pump, passing the feed pipe from your expansion tank via an air separator, vent pipe, then to either a 3-port motorized valve or splitting off to 2 separate motorized valves, one pipe going to the coil in your cylinder to heat your hot water, the other to your rads.

Does your current programmer have an option for just central heating but doesn't function that way or does it just not have it? Do you have the 2 motorized valves or just the one 3-port one?

 

[Bon]

Are you sure it's fully pumped heating & DHW and not pumped heating with gravity DHW?

My old system had a similar controller and was set up this way.

As Geegas says, it's all about what happens between your boiler, pump and cylinder rather than the individual pipe runs through your house.

 

[East Kent Coastal]

Ah, yeah. Gravity DHW. How many pipes are coming from your boiler? If it's pumped CH and gravity DHW there'll be 4.

 

[MANDATE]

Can't see how your system is fully pumped if you can't have CH only.
Fully pumped means all the heated water goes through a pump. then its divided so both CH and HW can work either together or separate, controlled by a mid position motorised valve or two 2 port valves.
I would think your system has pipe work where the HW is circulated by gravity. The CH side may come the same pipework but with a pump installed to circulate the water. The pump will normally be controlled by a room stat.
When tracing and identifying pipes, you need to note 'size' of pipe, its position relative to other pipes or other features and it's temperature.

If you put HW only on and feel the pipes you'll soon know which is flow and return.
If you gave more detail like make /type of boiler, existence of room stat, cylinder stat

 

[andrew45]

Thanks for all your help so far.

I've checked the boiler & pipes coming out. There are 4 pipes connected. One goes to the pump situated near the boiler, gets hot pretty quickly and I strongly suspect feeds the radiators. One of the other pair gets hot slowly and I think goes upstairs to the hot water tank and also in parallel the bathroom towel rail.

There is a room stat in the hall and a stat on the hot water cylinder. The boiler is a Ideal Concord W Gas Boiler, Model WRS255A.

So is it fair to assume that the system is as Bon suggested, pumped central heating and gravity hot water.

The controller is a Randall 3060, and when it is set to the only setting to have HW only (called 'H off, W twice') the boiler doesn't come on. Is it the case that the thermostat on the hot water cylinder will turn the boiler off when the water is at temperature - in which case the boiler may not be coming on because the hot water tank is at temperature.

Given all the above, and maybe some changes, would it be possible to get the system to perform the following:
- Heating without hot water.
- Hot water on its own.

Many thanks for your help.
Andrew

 

[Bon]

Hmm, I'm not an expert on those boilers or that programmer, but I would think you're fighting a lost cause.

You are correct in assuming that the boier DHW circuit will shut down when the cylinder stat is satisfied.

It also sounds if whoever installed was thinking about it as if the towel rail is fed from the DHW primaries, it means that it will get hot when the DHW demand is on so you will get warm towels all year and not just when your heating is on.

 

[D_Hailsham]

There are 4 pipes connected.

Yes, that's a pumped CH, gravity HW system

There is a room stat in the hall and a stat on the hot water cylinder.

There should be three wires (plus earth) connected to the HW cylinder. If there are only two wires, that the reason for you not being able to use position 6 on the timer.

The 3060 uses a common timebase for both CH and HW. This means that you are restricted to common times for CH and HW. You can use the selector switch to make changes to what is on/off, but you cannot have fully independent CH and HW control, e.g HW from 4am to 6am, heating from 6am-8.30am. If you want that, you will have to install a dual timebase programmer.

You would also need a V4043H motorized valve on the pipe from boiler to cylinder. It looks like this:

View media item 11762
This will turn your system into a C Plan system.

View media item 827 View media item 73
If the towel rail and cylinder are in parallel, like radiators, and the motorized valve is on the return between the cylinder and the towel rail return, the towel rail will still warm up, even when the HW is off. But if the towel rail and cylinder are in series, the towel rail will only get warm when the cylinder is heating up.

 

[andrew45]

Thanks D_Hailsham, your advice is really useful.

I think the thermostat on the HW tank is currently just used for the immersion heater, so the water gets to whatever temperature the boiler is set at, and that is really too hot.

Is it possible to use this same thermostat to control the C-Plan that you outlined, i.e. have one thermostat controlling two things neither of which will be on at the same time), or do I just strap another thermostat to the tank?

Thanks again for everybody's advice, it is all a lot clearer to me now.

Regards,
Andrew

 

[Nige F]

Thanks D_Hailsham, your advice is really useful.

I think the thermostat on the HW tank is currently just used for the immersion heater,
Thanks again for everybody's advice, it is all a lot clearer to me now.

Regards,
Andrew

The immersion Heater has it`s own stat inside the cover @ the top :

 

[D_Hailsham]

I think the thermostat on the HW tank is currently just used for the immersion heater, so the water gets to whatever temperature the boiler is set at, and that is really too hot.

If your cylinder stat looks like this and is on the side of the cylinder you can use it for the C plan:

View media item 10596
But if the stat is at the top of the cylinder it will be the immersion heater stat; and you can't use that; you need one like the pic.