Confused by cental heating plumbing

[puzzled-duo]

A friend recently started to have problems with his central heating system (CHS).
There are two boilers, being an oil fired boiler and pump (P2) in an outhouse and a back boiler around the living room fire. There is a second pump (P1)which is in the Airing Cupboard.
Each pump has its own thermostat and whilst P1 in the Airing Cupboard has a manually operated electrical switch the pump in the outhouse, P2, is wired so as to come on with the oil fired boiler.
My friend was told NOT to run both pumps simultaneously as they interfered with one another.
The visible plumbing for the CHS is depicted in the attached diagrams, the remaining CHS plumbing is buried under the bungalow's floor or in the walls.
The radiators seem to be in parallel with one another i.e. they all warm up simultaneously and shutting off any combination of radiators does not effect the remaining radiators.
Given the size and number of connections to the hot water tank (HWT) I assume there are two heating coils in the HWT, is this usual? However we do not know how the left hand heating coil is connected to the rest of the CHS.
We found the 1/2"? venturi? pipe in the Airing Cupboard to be clogged, after scraping out the sediment in that pipe the back boiler no longer "boils".
My friend wanted to change the corroded and seized stopcocks in the outhouse and I noticed that P2 was drawing from the bottom of the boiler. In what may turn out to be a Homer moment I suggested that it might be better to reverse P2 so that it feeds the bottom of the boiler and we added a oneway valve.
At the moment the oil fired boiler now rapidly trips its thermostat (which it did not previously do) and I suspect that when the oil fired boiler and its pump are running the new flowpath is trying to push water the WRONG way through the one way valve in the airing cupboard.
Although we are uncertain whether the flowpath from the oil fired boiler has an as yet undislodged air lock I suspect that what we/I should do is reverse the connections to the boiler, as depicted in the diagram "Outhouse oil fired boiler (proposed flow path)", so as to draw from the top of the boiler rather than the bottom of the boiler yet restore the original flow directions in the plumbing connecting the outhouse to the bungalow.

Suggestions as to the fix for the current situation would be most welcome as would a likely diagram for the whole system.

Thank you.
Probably Homer.

 

[ReJect]

My advice is do not touch something you know nothing about, sorry.
The solid fuel boiler is dangerous if plumbing is messed about with.
Why has your friend not brought in a professional heating engineer who is experienced in dual heating systems.
I have been installing such dual systems for nearly 40 years and ordinary systems prior to that and they are not for anyone inexperienced to work on, including many plumbers tbh.

Oil fired pipes to cylinder could be from main rad circuit.
Injector tee is a method of doing solid fuel pumped to aid gravity circuit

 

[puzzled-duo]

Thanks ReJect and I accept your points.
With regards to the solid boiler, other than cleaning what you might call the "injector tee" that boiler's circuit has not been fiddled with and now seems to be working correctly. If I understand your safety concern correctly (pressure build up) this boiler is vented.
The above said, since you are experienced could you suggest a plumbing diagram? A diagram would be useful to us even if we just restore the original connections and the diagram is just used as a reference.
With regards to why has my friend not called in a pro, we both like to tinker and learning about the system is always benificial.

 

[ReJect]

The pump at oil boiler should be pumping the water in the direction of exiting the boiler flow.
Either pipe (flow or return) would work on your diagram to have pump fitted if it pumps towards boiler if fitted to return pipe or pumping away from boiler if on flow. Check valve would also have to be for open on correct direction of flow obviously.
The pipes coming from floor could be wrong at oil boiler and mixed up. That would cause the flow wrong direction at other pump and other check valve.
You need that checked out.
Also you could have airlock in system.
There will be an extra pipe you haven’t drawn - a pumped flow from the fire I would think.
Obviously hidden due to being at fire and buried in floor.
Fire would normally have 3 pipes from it, going to 4 by using injector tee.
Seriously don’t tinker with heating systems unless you know exactly what you are doing.

 

[puzzled-duo]

Ta.