UK central heating plumbing and control questions.

[CMW]

UK bungalow built about1975. Central heating installed professionally when the previous owner had it built. Query is re hot water cylinder heated by oil fired central heating boiler and with immersion heater and separate thermostat.

I have never really got to grips with how the system is supposed to work. It has two pumps, but the second *MAY* have been added when an upstairs room was added after the bungalow had been built and in use for some years. Both pumps run when the central heating is on under control of the programmer. In the piping to the water heating coil in the hot water cylinder is a two port zone valve. Currently it's seized up, either the motor or the valve itself, so I guess that's why neither the boiler and neither pump runs when the hot water is turned on at the programmer.

Why is there just a single 2 port zone valve? How might it work, if it's open is it designed for the main pumps to flow water through the heating coil as well as the radiators based on pressure differentials?

There are no room stats. Every radiator has a thermostatic valve on it. The boiler has a built in thermostat control. The bathroom towel rail is always flowing so would act as a bypass, I don't see any pipe based bypass for water to flow if all rads are turned off.

Finally, when it was working, if the hot water was turned off at the programmer, but the central heating on, the water in the cylinder rose to very high temperatures over a couple of days. My thoughts are the zone valve is leaking or it's micro-switch and / or thermostat are wired up wrong and the hot water zone valve is opening and water at central heating circuit temperature is flowing slowly through the coil without proper flow regulation.

I'm puzzled, fitting a three port valve or a second two port one would be a real challenge , there's very little space and it already looks like a snake charmers nightmare.

Thanks for any ideas. Have you come across a system like this with just a single two port zone valve?

 

[Exedon]

Clear pictures of pipework showing pumps motorised valve and pipework layout would be useful.
Oil systems of that age often used 2 pumps wired through relays.
Systems with a single zone valve were also not uncommon.

 

[ericmark]

The C-Plan over the years was modified. The original no control over DHW, if central heating on, it would heat DHW, the second allowed one to use boiler in the summer, to heat DHW, and the final allowed one to control DHW summer and winter. There were special programmers, with switches and sliders for other Plans they were called 16 programs, and for C-Plan 10 programs, they counted off as a program, a bit of a cheat really.

I have the original C-Plan, but someone it seems thought if they used two pumps, they could select granny flat or main house, this did not work, use one pump, and it flowed backwards through the other pump.

My heating guy tells me not to heat the DHW can cause over heating of the boiler, my pumps are on the return, so a by-pass valve would not work, so it is a bit of hit-and-miss to if the pump stops when no demand, the boiler not a problem as said it will heat the DHW, but the pumps could cavitate I don't really have a way to stop it. I will guess there is some by-pass somewhere, but never found it.

Now with PV solar panels, the immersion heater in summer is cheaper to run to the boiler, I found it needs around 40 kWh to heat DHW with oil, and under half that with electric due to losses boiler to tank, I can switch only boiler on, but I don't, and it has saved a heck of a lot of oil.

Even without off-peak, and solar, it can't be very much different between the two ways of heating DHW in summer.

I used programmable TRV heads in the last house, with gas modulating boiler, and it worked very well, they would keep rooms to within 0.5°C of setting, but here with a simple on/off oil boiler nowhere near as good, but it does work, but clearly if boiler not running the radiator can't heat up.

How to turn on the boiler, is open for debate, the theory of using linked TRV heads seems good, but in practice many of my radiators are on outside walls, so tend to be cooler to the room in general. And with non linked, it is how to ensure boiler runs when required.

I have a mixture, for main house two wall thermostats, and one linked TRV head. But Wiser not really designed to work with C-plan, and Nest Gen 3 will not link to TRV heads, so neither ideal, but together they seem to be working.