Night storage electric boiler

I am surprised your electricity bills are so low considering it is your only source of power. It is supposed to be the most expensive way to heat your home, but your bills seem lower than many people get on gas, never mind oil.
Economy 7 may no longer exist, but many suppliers offer its successor, Economy 10, giving you savings on off-peak electricity. There is no doubt that electric heating is one of the cheapest in terms of capital costs, but the theory is that you pay for it later in running costs over the years. Alternatives like a heat pump will require a very substantial capital investment and work best with underfloor heating, not radiators, so you would have even more costs if you wanted to take advantage of this green technology.
How about you just add some electric underfloor heating mats in the new rooms. These are inexpensive at £300-400 per room and are easily fitted and would leave your existing heating load - and boiler - unaltered. For electric UFH suppliers check out the directory pages www.homebuilding.co.uk/directory

Michael Holmes is the Editor-in-Chief of Homebuilding & Renovating, Real Homes and Period Living magazines, and presenter of several property TV shows. He has self-built three times and renovated over 25 houses, and is the author of Renovating for Profit

I see the comment from Michael Homes that £85 per month appears cheap. I have a 5 bed house that I have lived in since November 1989. We purchased it new. Our monthly electricity bill to cover heating, cooking, lighting and general power is £65 per month. That is established over a number of years and set by my provider based on meter readings over the last 18 years. So £85 does not sound too low to me.

Hello, bit of an old post but we have a Nightstore 100 in a four bed detached.

It is brilliant. But. Up until very recently - months - our mains voltage has been around 254V, it has just dropped to 230V. This has had a real impact on the amount of energy the boiler can store, as expected.

I am currently running tests on it to see if it is 100%. So far the heating current is 37A per half (there are two separate charging circuits inside) giving 17KW total. Over the seven hours is stores about 119KWh of energy, so is on for 100% of the time. During charge the house heating is also on for about three hours, this will take heat from the core.

With a chart recorder attached to the thermocouple there is a nice linear rise in core temperature during the charge, and a similar slope downwards when running the heating. Maximum core temperature is about 650 deg C, maximum core temperature is 750 deg C, so not there.

We are running 9 radiators, others are turned off. We are in a windy place, on the top of a hill with plastic double glazing. Quarterly energy consumption in winter is over 9MWh. I reckon, at the moment, that running it in boost when needed, 11.5p/kWh, is still cheaper than buying another heat source such as gas. Possible middle course is to get another night storage heater, 2.7 kW or so, and use that as a top up.

If the house was being built then the best choice is under floor heating, only needing 50 deg C maximum water so a heat pump would also be a useful source of heat in autumn and spring. But I am not about to dig all the floors up!

Any comments?

Bob

Hi, i cannot believe some of these comments about the nightstor 100.

i have moved into rented accomodation for the last six months, 4 bed detached house, and apparently by bill so far is 1,500.00. i have tried every line of enquiry and yet they say this is correct?

our nightstor 100 failed to distribute heat after being switched on. Hyndburn engineering were brilliant and so helpful. i would reccommend talking to them if you have any problems. A new fan motor was fitted-not cheap, but considering no annual maintainance costs, thats acceptable. Our heating costs are around £130 per month for a 4 bed detached bungalow-which seems high reading other comments, but it will be interesting to see if the new pump makes a difference.

A repeat post after reading others comments, thanks.

I mentioned that the maximum energy storage in the 100 is about 120kWh over the 7 hours. If you are using more than this then you are boosting, running it on day time rate electricity. Just keep an eye on the electricity meter, or more easily buy one of those Owl consumption meters. I have one attached to the boiler and after checking against a Sullivan dynamometer wattmeter it seems pretty accurate, 1-2%.

With the just ended cold weather it has kept our 4 bed detached warm, internal temperature about 19C, with only minimal boosting, about 10kWh, on days at -11C.

One problem that has become more apparent is it not taking a full charge overnight. At 2am you can hear the contactors clickong in and out, end up with just 40-50 kWh stored, house is then cold. Investigating this I realised that the idiot who wired it up connected the boiler and the other cheap rate loads, immersion, outside storage heaters etc all on the same phase. This meant it was supplying well over the 100A rating. I rewired it so the night signal operates the boiler controller through a relay, and split the phases. It is well worth checking how your boiler is connected.

I have the maintenance manual and have partially traced the circuit of the controller. I have also tested the capacitor values due to the controller getting extemely hot. All capacitors are ok, much to my surprise. When looking at the clicking in and out I noticed that gently pushing the contactor would result in it being pulled in, the other contactor would then also pull in. The contactors run from the 30V DC supply, and I thought it might be low or the smoothing cap dying. At the moment the mains is about 117V, so well down from the design 240V. The is no voltage rating on the contactor coils that I can see, but the fan and pump are 22V. I have dug a scope out to look at the waveform on the smoothing cap but not woken up to do so yet!

I have found that the cables get very hot, even with all the screws fully tightened. Not helped by being in with the boiler and cable buried in the plaster. Alternative wiring arrangements could be a good idea. I also had the original controller isolator switch burn out, and this seems to have oxidised the copper cable, I am investigating whether it needs stripping out and replacing.

All in all I still think it is an excellent heating system. I would be interested to know exactly where other peoples' electricity bills are going. For example £3500 pa seems impossible unless it is running only during the day, you do have cheap rate 7 hour electricity?

For repairs to the elements talk to people who repair electric furnaces and pottery kilns. The elements are consumables and can't be that expensive. Similarly the crimps have to be nickel, see similar suppliers or people like RS components. But they MUST be crimped TIGHTLY! Having said all that, I bought in some spares and have not needed to replace anything, and it is now over 20 years old.

Te secret to using the Nightstor is to understand it, buy one of the wattmeters and record what it says, during the say and night and also longer term.

Please keep the comments coming, they are really useful.

Bob

We have a compact 45 boiler in a 4 bed detached running 11 radiators. Our bill is £187 pm (no gas).We run on E-on's Heatwise tarrif which gives cheaper (not as cheap as economy7) electricity for 2 hrs in the afternoon, 2 hours in the evening and 3 hrs early morning, Its sounds like most people run these boilers on E7. Maybe I should go to e7 but I have always assumed that the bioler would run out of heat by late evening. Seemingly this is not the case? Does anyone know of anyone who repairs these biolers who is based in Lincolnshire?

Does anyone know whether the Nightstor 100 contains any asbestos. We would like to replace it this winter and a plumber has asked whether I know.

Does anyone have or know where i obtain GEC Nightstor 100 Manual please? Many thanks.

Hi, been busy insulating all summer so not looked at this thread for some time.

How can I communicate with others privately about the Nightstor 100 manual?

Bob

Can anyone put the information together as a simple abc how Nightstor is supposesed to run ie set dials on timer controller etc.What is reset switch fo on boiler?

An update on our Nightstor 100 boiler. Last winter we were starting to get night s when it wouldn't store the requested charge. Looking at it in the early hours of the morning and the main relays would keep flicking in and out and completely random intervals, seconds, minutes.

Did nothing over summer, but this winter it was doing the same so had a closer look.

Tracing the signals back it was apparent that the 'charge' signal on U7/13 was flicking high and low, traced to the 'allow charge' signal on U4/1 being the culprit. This is a comparator comparing the core temperature with the voltage from the charge control pot.

Further tracing of the circuit came back to U1/1 and U1/7, these are the op amp outputs from the core thermocouples. In my case U1/7 was flicking from a sensible voltage, varying from about 2V to 5V, down to 0V. This was caused by the thermocouples going open circuit and R3 pulling the op amp input to +12V to shut the boiler charge off.

Taking the control board out of the case and inspecting it came up with a hairline crack around pin 1 on PL6, the thermocouple connector. It wouldn't resolder, the pin seems to have suffered from an intermetallic bond corrosion between the brass pin and the tin plating. I had to file the pin back to bare metal before I could tin it and complete the soldered joint. This intermetallic failure is due to high temperature, out controller is in a small cupboard with the boiler and it gets very hot.

This seems to have fixed the problem, boiler taking the charge requested.

As additional help, the boiler thermocouples on U1/1 and U1/7 will give a voltage range from about 2.25V (maximum heat) to around 5V (boiler just about cold).

Also, the night signal is detected through OPT2 to turn off U6/11. U6 is a NAND gate, and when no night signal its output is low, U6/13 pulled up by R68 and U6/12 by R70. R70 and C23 are a power on time delay and after a few seconds play no further part in operations. The problem is R68, R69 and C22 connected in series. Normally R68 and R69 pull U6/13 high. When the night signal appears then the opto coupler OPT2/5 pulls the junction of R68 and R69 to 0V. The snag is that this signal is actually a 50Hz sqare wave due to the 50Hz mains. This results in U6/13 dropping to about 3V, which is comfortably in the logic gate transition voltage. This makes the gate an amplifier and noise can possibly cause it to randomly switch. I paralled R69 with a 12k resistor to reduce it value to about 10k. This makes U6/13 voltage about 1.2V, a little high but much better than before. If you have random switching problems then this might be a solution.

Hope this helps.

Bob