Hot Water Problem

[Susi00W]

Hi
I would be very grateful to receive some ideas to resolve a problem I have with my hot water.
I have 2 large Heatrae Sadia Megaflow cylinders fitted that are now around 12 years old (They are 250 or 280 cant recall which) Overkill for the house really!
There are 2 immersion heaters fitted to each tank one at the top and one at the bottom. I understand the top one is a boost.
Strange as it may seem there were no timers fitted to them originally and they were just permanently on. When times started to get hard, 2 years ago I had central heating timers fitted to each one.
Since then they hot water constantly trips out at the sensor on the thermostat fitted to the cylinders, maybe 3-4 time a week.
I phoned Heatrae and they said the water temperature is probably too high and is causing the heat sensor to trip out so I turned them down to a much lower temp and it continued to trip.
I phoned Heatrae again and they said it probably needs new thermostats so I had new ones fitted. It continues to trip out. I didn't replace the immersion heaters
So my questions are:
1. Has anyone come across this before and found a solution? If so, please help
2. I'm wondering whether to remove one tank and replace with an electric water heater but is there an effective electric instantaneous water heater that will provide enough hot water for three bathrooms with power showers. (There is no gas in that part of the house and it would be expensive to run a supply due to vaulted ceilings and no void to run them) I do have 3 phase electricity.
3. Is there a better solution I haven't thought of? My house is up for sale and I need to resolve this for the next owners but keep the cost reasonable.
Thank you for any ideas and feedback
Susi

 

[stem]

I have come across it before, but turning the thermostat down slightly resolved it. The overheat trip is there to switch off the heating element if the thermostat fails in the 'on' position in order to prevent the water in the cylinder boiling.

If the thermostat is turning the heating element off at the correct temperature all should be well, but as you have changed the thermostat and the problem has remained, then I can't see what else it could be than the overheat switch tripping too early. I'm assuming that the trip is a separate item from the thermostat and so wasn't replaced with it.

Do you have the same problem with all four immersion heaters?

Domestic instantaneous water heaters are only capable of one normal shower (they cannot be used with a power shower pump) or sink, but certainly not a bath. As you have a 3 phase supply, you may be able find something industrial that will do the job, but it won't be cheap. As it stands, the price of new immersion heaters should be less that £50 each, and they are simple to fit once you have managed to get the old one out.

 

[Susi00W]

Hi Stem
Thank you for your reply. I have the same problem with all 4. The overheat trip is on the thermostat so these got replaced and are all turned down. It seems to me to be the timer that causes it to trip.
It is driving me to despair. Other than having the water on all the time 24/7 I don't know what to do to rectify it.
The cost of the immersion heaters for the model I have is £120 each (x 4) they come with a new thermostat as part of the immersion, plus labour but Im not convinced it will solve the problem. I could buy one new cylinder for that.
None of my showers have pumps as they are all fed from the Megaflow (a pressurised cylinder).
Regards
Susi

 

[Dan Robinson]

Hard water area?

 

[stem]

Unless they are wired incorrectly, the timers won't cause the problem. All the timer is, is a switch. It's either 'on' or 'off' yet you say the problem doesn't happen when they are on 24/7. This is really odd. Immersion heaters are the simplest form of water heating and don't usually suffer from bizarre faults.

I thought it was unusual to have a "power shower" fed from a Megaflow.

 

[Susi00W]

We are in a hard water area- ish but I have a Wizzard thing (wire coil) fitted to the mains inlet pipe that is supposed to remove calcium.
It is a real mystery!!
S

 

[picasso]

Are you running all 4 immersion heaters at the same time ? what is the make and model of the timers ?

 

[Dan Robinson]

We are in a hard water area- ish but I have a Wizzard thing (wire coil) fitted to the mains inlet pipe that is supposed to remove calcium.
It is a real mystery!!
S

Did the Wizzard thing come with a free barrel of snake oil?

 

[Susi00W]

It makes no difference if I have just one on or 4 they all trip at various intervals. One top one is better than the other three, I end up using this one all the time as it will go a couple of weeks without tripping but it just does just one shower. We then wait for it to heat up again for the next person...really bad given I have approx 500 litre capacity!
The timers are from YESS Electrical, so should be a decent trade brand.
I didn't get the free snake oil, I must chase them and complain

 

[Susi00W]

It makes no difference if I have just one on or 4 they all trip at various intervals. One top one is better than the other three, I end up using this one all the time as it will go a couple of weeks without tripping but it just does just one shower. We then wait for it to heat up again for the next person...really bad given I have approx 500 litre capacity!
The timers are from YESS Electrical, so should be a decent trade brand.
I didn't get the free snake oil, I must chase them and complain

 

[Susi00W]

It makes no difference if I have just one on or 4 they all trip at various intervals. One top one is better than the other three, I end up using this one all the time as it will go a couple of weeks without tripping but it just does just one shower. We then wait for it to heat up again for the next person...really bad given I have approx 500 litre capacity!
The timers are from YESS Electrical, so should be a decent trade brand.
I didn't get the free snake oil, I must chase them and complain

 

[Susi00W]

Any Derby based plumbers/heating engineers looking for a challenge!!?

 

[Dan Robinson]

It won't be much of a challenge - 4 heavily scaled immersion elements to swap an the thermostats to be set correctly.

 

[simond]

The Megaflo has had a number of different thermostat arrangements and immersion heaters over the years, the early cylinders were made by Fabdec for them.

http://www.unventedcomponentseurope...sadia-megaflo/megaflo-airgap/hs-95612026.html


http://www.unventedcomponentseurope...a-megaflo/megaflo-airgap/hs-95606920-oem.html

One of the older models here;

http://bvra.org.uk/documents/heating/Megaflo Hot Water Cylinder.pdf

Best is to remove an immersion from the cylinder and see if it is all scaled up, chances are it is. If it is the later type, there is a metal U shaped tool that was supplied with the cylinder that you'll need to get the immersion out.