How to find circulation fault on central heating?

[ericmark]

Boiler cycles in winter, with return pipes hot, but no radiator seems to have a very hot return, pump on return and no by-pass found.

I suspect some thing hidden by the plaster board put up when the garage was turned into a flat, the whole system was a mess when I moved in, two pumps, one thermostat, and one programmer, three FCU's and a socket outlet from a consumer unit and a fuse box, so it seems the central heating was not used much, and main heating was an open fire burning wood.

Seems installers had thought using one pump for flat and one for main house one could select which was heated, that was not the case, all selecting which pump was on did was select direction of flow, I got a plumber to fit zone valves, and thought he would just use one pump, be alas he left it with two, so the thermostat works the motorises valve, who's micro switch works a relay, one set of contacts works the pump, the other set the boiler, so two relays so can select which pump runs.

But heart of winter the living room radiators are warm but not hot, as are most radiators in the house, but the boiler is cycling, so not giving full output.

Since working on a C plan could be the DHW, except DHW is connected to other side of boiler to CH, and CH return pipe is hot, so it seems water is circulating though some pipe work unknown to me, and I am not sure where to look.

Note oil boiler which does not modulate.

 

[Mottie]

Bypass open too much?

Edit, ignore that I see you have not found one. Are you 100% sure though?

 

[oldbutnotdead]

Dhw on the other side of the boiler- is this an older boiler with 4 outlets?

That aside, given the complexities of multiple pumps you may need to hack the pb off to see what you've got and start making some sense of it all. Pics always help....

 

[ScottishGasMan]

If return pipes are hot then you either have:

at least one radiator that is roasting and flowing hot back to boiler(often a towel rail), OR there is a by-pass of some description hidden somewhere.

Water will take the path of least resistance, so I'd be looking for where the hot return water is coming from first. If it is a bypass, you need to get it closed down first to see how much actual circulation is possible through the system. It could be closing the bypass forces water round the system and it heats up much better, or if there is also system restrictions then the boiler wont be able to get rid of its heat and cycle more or overheat, either way you'll have a better picture of whats going on in the system