Old back boiler and electrically heated water - energy bills

[DIY10291]

With all the energy price rises, I am reviewing my energy wastage. The CH in my house is a (very) old Baxi Bermuda back boiler. The heat exchanger was replaced around 5 years ago. It hasn't been serviced since, and occasionally the pilot light has gone out and I've had to relight it a few times (though it was fine last winter after moving the sofa out the way. Anyway I understand a new thermocouple is quite cheap). Other than that, the heating works acceptably well (though the whole system is old, including all the radiators, so they are sludged and the header tank is currently infected with some kind of bacteria or fungus, but that isn't the fault of the boiler).

The HW is a bit messier. The boiler has only been wired to respond to CH needs, so in the winter whenever the CH requests heating, the hot water is also heated. But this is unreliable, so the immersion ends up doing most of the work (and, in summer, it does all the work because the CH needs to be switched off). The electric controls have not been sorted to fix this; there is an electric zone valve fitted but it isn't wired up to anything.

I haven't had this fixed yet mainly because I don't know any plumbers (West London) who would work on a back boiler/electrics, and am unsure of what is worth doing. My energy usage is around 14500 kWh gas and 5000 kWh electric (3 bed house). The national averages for a 3 bed house are around 12000 kWh gas, 3000 kWh electric. Current prices: 28p per kWh electricity and 7p per kWh gas.

Assuming (big assumptions, but I don't have a smart meter) the extra 2500 kWh gas is a result of the inefficiency of the boiler (though we also do more cooking than the average household), that's a wastage of 2500kWh x £0.07/kWh = £175/year on gas.

And assuming the electric is all because of the immersion (though we do use the kettle a lot, so that could be part of it), that's (5000 - 3000)kWh x (£0.28 - £0.07)/kWh = £420 on electric.

So, my options are a) do nothing, b) get the boiler working on HW (and get it serviced, possibly with a new thermocouple), and c) get a new combi.

From these numbers, and with prices always rising, it looks like I should at the very least get the HW off electric. Whether to change the whole thing is a bigger question; it's a shame to be wasting gas with an old boiler, but it's been reliable despite years of neglect, and a new one may not pay for itself anytime soon. What do you think?

 

[oldbutnotdead]

Your big problem is that the back boiler has been plumbed in as a direct replacement for the original coal-powered water heating back boiler- gravity circulation to the cylinder, pumped circulation for the heating.
This type of setup can operate on hot water only or hot water plus heating but not heating only.
If you can't select hot water only then the controls haven't been set up properly. If you have a zone valve not connected to anything it won't be helping.
If you have zero DIY skills then the most cost-effective solution may be a full system replacement. Best get a couple of local heating engineers (NOT BG or any of the 'big' installers, avoid CheckaTrade etc., see if your local Trading Standards run any sort of Trusted Trader scheme) to have a look at what you have and advise on your options
If you have (or want to acquire) some DIY skills then your back boiler can continue its faithful service for many more years. No it won't be as efficient as a modern boiler but you can improve the overall system efficiency and comfort delivered with a fairly small investment in time and control gear.

 

[ianmcd]

The heat exchanger was replaced around 5 years ago. It hasn't been serviced since,

These are great boilers, but you MUST get them properly serviced every year, important that you get it properly serviced

 

[ericmark]

Interesting as I also have a C Plan, when I moved in the timer (programmer) had a three core cable and earth between it and boiler, but changed colour and one core open circuit. And no thermostat on the cylinder, other than one built into the electric immersion heater.

So step one was to make it so the pump and boiler can be energised independently so boiler can run without the pump, two methods open, wireless links, or using the pair of wires to both send power and information down them, I went for latter, not sure this was best option, but the time clock was removed, and the wires between it and the thermostat linked, so from the thermostat or may be better called a controller, to the relay box or heat link as Nest calls it, I have two wires that keep the thermostat charged, and send info to the heat link.

So now I can select down to ½ hour and which days I want the boiler to fire, where the old time switch the minimum run time was 1½ hours, and every day, or not at all, so now set to run 4 times a week ½ hour each time, but there is no thermostat, so a bit hit and miss, we get warm water to wash our hands, but it may not hit the 60ºC needed to stop legionnaires.

I have studied the house, and to get a cable from water tank to boiler is a mammoth job, so either some wireless link, or a timer on the immersion heater. This is still to be done.

So using a timer I could set it to start after the boiler had just stopped, so it boosts the water temperature once a week to over 60ºC. Or I could use some thing like Sonoff to send a signal to the boiler, but the question is which is the cheaper to run, and by how much?

It is easy to say electric costs this and oil costs that, but when the boiler runs, it heats the pipes up three floors, so there are losses from the pipes, boiler runs for 20 minutes approx, as it reaches the boiler cut off temperature and switches off before the ½ hour has completed, so 18 kW boiler runs for 1½ hours a week to heat water to wash hands. And I need to run off cold to get the hot water to taps. So around 27 kWh per week, how many kWh would I need electric to run for? Likely less as no loses from pipes and boiler.

But we use three sets of taps, there is a forth but rarely used, would a small local water heater be better? And simply don't have hot water to as many taps?

What I have yet to work out, is my oil bill for a three story house is less than the gas bill was for a much smaller house.

Although I use Nest Gen 3, I would not recommend it, mainly as it has no remote sensors so only controlled by hall temperature, seems USA version there are remote sensors, but not UK version.

It is not the heating up, easy to control that with TRV's and lock shield valves, it is the cooling down which is the problem, the hall cools too slow.

 

[ericmark]

occasionally the pilot light has gone out and I've had to relight it a few times

I had this with the DHW boiler, lost count of how many sensors I had to fit, but the CH boiler ran seamlessly for years, had to get the flame hight adjusted once, and once the extra low voltage transformer burnt out, but in the main trouble free.

In the end one started to leak, so changed both with one combi boiler.

However the old boiler was simple on/off, the new boiler modulates, son lives in the house now, so don't know how it is doing, my worry is one radiator does not have any restriction on water flow, output controlled by fan speed, which is thermostat controlled. I have considered fitting a second thermostat set an little lower, which would short out the speed resistor, making it two speed, but now down to son.

The circulating of the air in the room makes a huge difference, not sure which is best, circulating air speeds up recovery, but means warm air blows past windows and doors, in mothers house I could not believe have much temperature variation one could get in one room, now as writing this, two thermometers showing 23 and 19.2 degs C in this room, my attempts at geofencing did not go well, mainly as it takes so long to heat and cool the room, so set it to cool to 17 degs C but never drops that low, so is there really any point?