Sanity check on improving slapdash heating setup

[joethearachnid]

Hi all,

Long time listener, first time poster but this forum has been invaluable to me in my recent heating system exploits. I live in a late Victorian house with what seems to be a heating system installed in such a way as to save a bit of cash wherever possible. As far as I can tell it's a fully pumped open vented system but it seems to be only half of an S-plan - there's only a motorised valve on the heating pipe and the hot water is just fully open (though with a manual valve) and so the hot water is always on when the heating is on. The boiler itself is a Glow-worm Economy Plus that is fairly ancient but also had some repairs a few years back that ended up replacing pretty much every replaceable part so it should be good for a few more years. It's also an 8mm microbore system which is a headache in terms of cleaning and flushing through.

So far I have done the following:
-Added new drain-off valves to downstairs radiators (there were no drain-offs at all that I could find except one for draining the hot water cylinder and the boiler itself). Also replaced quite a few nonfunctional TRVs and shield valves that started leaking after they were adjusted.
-Cleaned out and gravity flushed everything several times with Fernox F3 and added Fernox F5. Lots of black sludge removed and the radiators seem a lot happier now.
-Changed the very basic boiler control panel for a Wiser smart panel. I'm not a big fan of the Wiser app but at least we have a thermostat now and more granular controls than on or off. There's only wires for the boiler on and the heating valve so for the winter I wired those both into the heating control and that usually meant we got enough hot water. Now that things are warming up we don't need heating as much I've swapped the wires so the hot water is wired directly to the boiler on, but it's still not an ideal solution.

I have some more works in mind but I wanted to get a second opinion before I started cutting into any pipework. The loft setup is below:

The damp bit of MDF below the expansion tank seems to just staining, it's not actually wet.

My plans are as follows:
-Replace the red manual valve on the outlet of the cylinder heat exchanger with a motorised valve so we can independently control hot water and heating. The manual valve has been useful for balancing the heat exchanger with the heating circuit when they've needed to be on together, but we only really use hot water for washing up so it shouldn't be running at the same time as the heating that often. I'd prefer to put the valve before the cylinder and leave the manual valve for balancing but it's a tight gap on the inlet and I could just replace the valve rather than needing to put in any new pipework.
-Install a cylinder thermostat and put it in line with the hot water valve control so it doesn't just run until the water is scalding.
-Run at least three extra wires from the boiler control panel to the cylinder so I can have heating valve control, HW valve control/cylinder stat, permanent live and return valve switch control for the boiler. Currently I only have N/E, heating valve and pump wires.
-I may install a Magnaclean or similar which should help to regulate the black goop buildup. I can't see a good accessible spot that's out of the way so I think the only option may be the return pipe directly above the boiler, which may look a bit fugly in the kitchen.

Questions on the above:
-Have I missed anything obvious? Am I building a pressurised bomb?
-Am I OK to replace the red manual valve as planned?
-Do I need to fit a pressure relief valve anywhere? There isn't a separate one in place currently and I'm not sure where the best location is if needed. I'm guessing after the pump but before the motorised valves, though I don't know where it should drain to. There is a PRV on the boiler itself and I'd be wiring it so the boiler/pump would be controlled by the valve switches. Currently the HW is always open so even if the motorised valve is faulty there's always a path for water after the pump.

Any advice is welcome, even if it's just "you're an idiot, call a professional before you hurt yourself".

Thanks!

 

[Mister Banks]

Im just a diyer so others will comment further I'm sure ......... The red gate valve is there to control the flow through the HW cylinder and needs to stay in place. With a bit of repiping you could fit a mid position valve just under the pump and have a y plan system. This will need wiring but you may already have enough wires when you remove the existing motorised 2 port valve. You will also need a cylinder thermostat if one isn't already installed. Y plans aren't optimal but better than what you have.

If this is an open vent system then no need for the additional pressure relief valve.

 

[CBW]

Yep as above, no need for a prv. If you install a motorised valve on the return then it won’t work how you intend and would be causing an issue. It looks like a C plan of sorts. You could upgrade to a Y plan or s plan if you cut the pump further back? I doubt you’ll have just N and E.

 

[joethearachnid]

Thanks both - reading into it more it looks like the balancing valves are more common than I'd realised and I guess especially a microbore system would need one. I'll try and put the motorised valve elsewhere or look at a Y-plan. Cylinder stat is definitely in the plans.

Chris - I have N and E wires plus live control wires for the valve and the pump, but no constant live and no other spare wires on the boiler 3A circuit. What would, in theory, be the issue with having the motorised valve on the other side of the cylinder? As long as there's a closed valve somewhere in the hot water run then there wouldn't be a flow through it, though I'd be concerned about debris collecting at the bottom of the heat exchanger while the valve is closed. I guess the pressure could cause joints to the cylinder to leak but only if the heating circuit was offering a lot of resistance or was completely blocked.

 

[CBW]

Just had a rethink/lookup and believe the motorised valve can be on the return. There’s must be a permanent live somewhere surely. Might be one from the existing motorised valve (mv).

 

[joethearachnid]

Shot of the current wiring:

Top is the pump with L/N/E
Left is the valve with N/E, the valve control wire (red) and the two orange and grey wires that would usually act as a switch for the boiler but neither is connected currently. My understanding is that usually you'd run a permanent live through the switch wires back to the boiler so it comes on only when the valve is open.
Right is the wiring coming in with N/E, pump control (red) and heating valve control (yellow). It's mad that they didn't run a few extra wires even just for redundancy... or install a motorised heating valve, or a cylinder stat, or a room thermostat, or even bother to put a drain off valve anywhere in the system. The more I've learned about heating the more I've understood that this installation is incredibly dumb, and apparently only for the sake of saving maybe £200 in total.