Possible C Plan heating system issues?

[volt hunter]

I am an electrician looking into a fault with a heating system that I haven't come across before. After research I think it's a C plan but not 100% sure. Theres a single hot water pipe from the boiler, to a pump, it then splits to hot water and heating with a motorised valve on the heating pipe only.

Apparently the valve got stuck and was replaced, but now the heating will only stay on until the hot water tank is up to temperature, then the valve closes. Can't seem to find any diagrams online that match the layout of this set up.

 

[CountryFan]

Have a look at this for diagram and wiring of a C-Plan. If it’s going off when hot water satisfied then maybe a wiring or timer fault?

 

[polesapart]

The Honeywell Wiring Guide is widely available online for download: includes C-Plan (p10 or thereabouts)

 

[volt hunter]

Have a look at this for diagram and wiring of a C-Plan. If it’s going off when hot water satisfied then maybe a wiring or timer fault?

I've looked at that, but it's a different setup. This one has the valve on the heating not hot water, and the pump is for both

 

[CountryFan]

Might have to see some photos then for clarity. I've not seen or heard of a system like that. Others who are more experienced may know.

 

[stem]

There are all sorts of hybrid systems out there. I've seen fully pumped systems that only have a motorised valve on the heating. There is a whole estate of bungalows built in the late 70's early 80's where I used to live that were fully pumped [Gravity HW circulation isn't an option for bungalows] with only a motorised valve on the Central Heating.

When the programmer was switched to HW only, the boiler and pump ran continually. Then when CH was required the motorised valve opened. It was not possible to have CH on with out the HW being on to keep the pump and boiler running.

This type of system doesn't have a thermostat on the Hot Water Cylinder because the boiler and pump have to run continually incase the heating is required.

A 'C Plan' on the other hand does have a thermostat on the Hot Water Cylinder.

 

[volt hunter]

The Honeywell Wiring Guide is widely available online for download: includes C-Plan (p10 or thereabouts)

There are all sorts of hybrid systems out there. I've seen fully pumped systems that only have a motorised valve on the heating. There is a whole estate of bungalows built in the late 70's early 80's where I used to live that were fully pumped [Gravity HW circulation isn't an option for bungalows] with only a motorised valve on the Central Heating.

When the programmer was switched to HW only, the boiler and pump ran continually. Then when CH was required the motorised valve opened. It was not possible to have CH on with out the HW being on to keep the pump and boiler running.

This type of system doesn't have a thermostat on the Hot Water Cylinder because the boiler and pump have to run continually incase the heating is required.

A 'C Plan' on the other hand does have a thermostat on the Hot Water Cylinder.

This sounds almost exactly the set up I have, except there is a thermostat on the hot water tank.

Good news is that I think I've fixed it, the plumber looked to have wired the valve back in incorrectly. Now either thermostat can bring the boiler on, but the hot water tank will be heated regardless if the central heating is on.

 

[fixitflav]

Can't seem to find any diagrams online that match the layout of this set up.

Info on here C-Plan might help

 

[stem]

This sounds almost exactly the set up I have, except there is a thermostat on the hot water tank.

Good news is that I think I've fixed it, the plumber looked to have wired the valve back in incorrectly. Now either thermostat can bring the boiler on, but the hot water tank will be heated regardless if the central heating is on.

Sounds like a Hybrid system. The Cylinder Thermostat will probably work to control the heating of the Hot Water only during the summer when the central heating is off, but when the Central Heating is 'on' it will override it and the Hot Water Cylinder will be heated whenever the heating is required.

 

[ericmark]

The C Plan in simple form has no motorised valve, or tank thermostat, it was used to heat the home before one got around to lighting the fire, the only way to control DHW was time, and in summer it was unsatisfactory, so a tank thermostat was often added this allowed use in summer, but did not help in Winter, then next stage was adding a motorised valve, this allowed cooler DHW in the winter. Of course, there are other options, this is my central heating been modified more since this drawing, I have a flat, which is why it has valves to turn off whole flat. Or whole house. I have added relays since that plan, but shows how the simple C plan can be modified.

It is rare to find C Plan with gas boilers, but oil boilers can last 30 years or more, so still found with oil boilers.