Need to optimise gravity HW & pumped CH system

[NetTechie]

Hi all, I've just moved in to a new house and would like to optimise / update the heating system without spending a fortune as we will be planning to renovate and strip out the system in a couple of years with something new. As it is today, the system comprises of the following components, going from top to bottom:

Loft - Feed & Expansion tank (insulated)
Loft - Cold Water storage tank (insulated, but not covered)
First Floor - Basic hot water tank with 4 pipes + a drain pipe (no jacket)
Ground Floor - Glow Worm Ultimate 40FF fan boiler with 4 pipes, gravity & pumped I presume
Ground Floor - Grundfos UPS3 fitted to boiler pumped return
Ground Floor - Old analogue themostat
Ground Floor - Siemens RWB2 Programmer / Timer

Now it's been a while since I did any plumbing as I've lived in new builds for the last 15 years, but now need to get this system sorted. Upon getting the keys, I realised the CH pump was jammed as the house hadn't been lived in for a couple of years. So off that came and a cleanup with some WD40 got the impeller moving again and the heating working. When I turn on CH the pump comes on but the boiler does not fire, when I turn on the HW the boiler fires up. Again if I have both on, it appears the HW is what causes the boiler to fire up and not the CH.

The major issue I have with this system is the amount of air that was building up, which I read maybe Hydrogen from the rust. So I flushed the system, wet vac the F&E tank to hoover up the 3 inches of rust coloured sludge left at the bottom, refilled and added Sentinel Rapid clean for 24hrs, flushed again and added Sentinel system restorer which I plan to leave in for a few weeks. At the same time whilst I had the system drained, I plumbed in a Magna Clean Professional 2 to the boiler CH return and the amount of gunk it removed in 24 hours was astonishing. The air (hydrogen) build up has been almost eliminated and the pipes sound much quieter.

The next problem is the controls. There doesn't seem to be any wiring centre or motorised valves that I can find on the system. There is no thermostat on the HW cylinder either, the system simply has 2x 2 core wires from the timer to the boiler. The F&E tank is always hot with steam coming off as the water is continually heated. My plan is to add a cylinder thermostat & jacket, a 2 way motorised valve to the HW return, wiring centre and a Nest Thermostat that I already own to get control of this system.

Now is this feasible and my only thought on this was what would happen once the HW return valve closes, can the boiler operate safely if the CH was still running being a gravity HW system. Is there anything else I should do / investigate to ensure the proposed changes are feasible and would it be worth it to control the system to save some money on gas usage?

 

[ericmark]

My oil fired system was the same, my major problem is type of floors so fitting new wiring or pipes was hard, and boiler was in the flat, but want to control from main house. So only two wires between floors so selected Nest Gen 3 maybe not the best option, but once fitted DHW does not need controlling in winter, and in summer would set ½ hour four days a week.

The Nest went where the wires went so mounted in the hall, it transpired not a good location, hall cools too slow, I thought it would work with Energenie TRV heads, alas no. So now have a Wiser hub in parallel with the Nest hub to get living room warm enough.

As time went on, I had solar fitted, so used iboost+ to heat DHW with an immersion heater in summer, this saved a lot of oil, I had not realised how much heat is wasted heating the pipes between boiler and cylinder, ½ hour was really 20 minutes, so 20 kW for 80 minutes is around the 25 kWh mark, but the electric was using more like 3 kWh per week, the heat escaping into the house in winter is OK house needs heating, but summer trying to keep house cool, I still can turn on the boiler to heat DHW but would only do it for a bath, as immersion heater only heats top of tank.

I found the 20 kW boiler is on the edge as to being big enough, so 9 programmable TRV's so I can select the rooms I want heating, I also manually in cold weather turn the temperature of CH water up, and as it warms up again I turn it down again to stop DHW from getting too hot.

The heating is far from perfect, but near enough, have considered new boiler, old one around 25 year old, but seems nothing wrong with it, annual service to set pressures etc, I have motorised valves so I can turn off whole lower floor as hardly used in winter, top two floors use the TRV's.

There is no published wiring diagram for Nest Gen 3 with C Plan, but this

works, it is basic how mine is wired. Note com to boiler.

 

[oilhead]

This is a very basic system by the sound of it. On a gravity H/W system heating alone cannot be selected. With the Hot water on and the boiler running, you can switch the pump to get heating. A room stat could control the pump and therefore the heating, and the boiler stat will control the flow temperature. In my opinion trying to adapt this situation temporarily would not be worth it. It needs a full conversion to either a Y plan, or probably an S plan, which would require less pipework alteration. You could then install whatever level of sophistication of controls you choose.

 

[ericmark]

I am not a boiler man, I employ some one to service my boiler when required, however he tells me with boilers which do not have a cool down sequence, to run them on an S plan can cause extra strain on the boiler, it relies on being able to cool by heating the DHW, so limited to C, W, or Y Plan. S Plan can cause strain on old boilers.

How true this is I don't know, but his advice was one reason for sticking with a C Plan. It costs a lot less to run to last smaller house with a gas boiler, so satisfied to stay with what I have. It uses around 200 watt of electric power, which is a little higher than I would like, but with a 6.4 kWh battery and around 4 kW of solar panels I have a reasonable chance with a power cut that it will still work. Depends when during the day the power failed.

I am very aware all the central heating needs to come from one FCU which is on the UPS, or from battery, so although the Nest Gen 3 can be powered from a USB socket, doing that would mean central heating would fail in a power cut.

Clearly heat pumps are non starters, as loss of electric power means they stop working, LPG means signing a contract with one supplier, and a large bomb in the garden, so until forced otherwise it will be oil. I have a grate which can be opened up easy, and oil filled radiator for any oil boiler breakdown, but I remember the dust with open fires, so don't what that if I can help it.

I look at the £1.5k for a new oil boiler, and my age at 73 and can't see a new one would pay. So unless it can't be repaired I will stick with it.