Boiler losing heat

[tabita]

Hi,
My boiler is a Heatrae Sadia Megaflo with 2 immersion heaters. The problem is that, I need 2-3hours of boiling time to produce sufficiently hot water. And even then, if I don't use the hot water at all, there'll be nothing left the next day.
Please help.

 

[noonespecial]

The Megaflo is an unvented domestic hot water cylinder and not a boiler as such.

Assuming it is only heated by the two immersion heaters and not by a hot water boiler system as well you could expect a 200 litre storage capacity unit to take about 2 hours to heat up.

So yours is probably about right. Let us know what the storage capacity is though of the unit and we can double check. You will find that on the label on the unit - or measure the height and tell us approximately how old it is.

If you run out of hot water you will have to switch the immersion heatres back on. Do you have a time switch? If so make sure it is correctly set for your requirements, particularly if you are using an off peak reduced rate electricity tarriff.

 

[tabita]

The height is 112cm, diameter 53cm. The label says DD145, probably more than 3years old. Both immersion heaters were replaced 2years ago.

I do have a time switch. I was just messing around with the switch yesterday (by rewiring them to 2 light bulbs) and i found out that, in the day, only 1wire has electricity, even if I press the boost button. And in the middle of the night, when it's off peak, the other one will come on. Never both. Is the about right?

 

[kevplumb]

get the heaters checked one may not be working

 

[tabita]

do i really need to get it checked? cuz a plumber can be so prohibitingly expensive! hahah, so hopefully i can figure out the problem, if there's one, from you guys

 

[JohnD]

The height is 112cm, diameter 53cm. The label says DD145, probably more than 3years old. Both immersion heaters were replaced 2years ago.

I do have a time switch. I was just messing around with the switch yesterday (by rewiring them to 2 light bulbs) and i found out that, in the day, only 1wire has electricity, even if I press the boost button. And in the middle of the night, when it's off peak, the other one will come on. Never both. Is the about right?

Yes, that does sound right. the off-peak will be on a timer so that it is automatically switched on when your electricity is cheap. If you feel the immersion heaters (the plastic caps, or the big brass nut where it is fixed to the cylinder) you should be able to feel they get hot when they are running.

The cylinder is not particularly big, but should be enough to give you a hot bath. Not enough to do washing up at the same time, though.

If you turn the upper one right off, then (as long as the off-peak one is working right) you should find the cylinder is full of hot water by morning. If not, it is possible that the immersion heater's thermostat is faulty or wrongly adjusted (replacing a thermostat is a relatively easy job, and does not involve plumbing as it there is no water involved - it is in a waterproof pocket).

You also mention the the hot water goes cold after a few hours? This suggests one or more of (1) a dripping hot tap wasting it (2) inadequate insulation (3) the water not being fully heated.

What sort of insulation does the cylinder and the pipes around it have? Has the insulation been pulled aside to keep the airing cupboard warm?

 

[Max32]

Hi
I have exactly the same heater and wonder where on earth can you get those thermostats. I've been searching and searching. Mine keeps blowing out every day and i have to reset the button on the bottom heating element every day. It is so annoying. I tried adjusting it, but no matter was setting it is on, it just blows out every night. I am aware it is relatively easty to replace them, but where can you get one???? Please help!!

 

[Timmyturtle]

A decent plumbers merchant will sell them.
I had experience of a DD megaflow last year where the water would only get slightly lukewarm
Eventually i found there was a leak in the Kitchen area (It was a Pub)couldnt hear the water running.
I tried replacing the lower Immersion heater before i discovered the leak.
I found the heater to be sitting in limescale up to its top.
The lime scale was labourously removed with a long handled spoon
All is well now
Can you hear the valve on the inlet making a noise even if everything is turned off..if so could be a leak somewhere

 

[meldrew's_mate]

There'll be a tundish on the outlet from the safety relief valve, if it's dripping then that'll be hot water escaping to drain, hence the overnight loss of hot stored water.
If this is the case regenerate the air gap by following the printed instructions on the side of the cylinder, or search for them using the power of t'internet.