Megaflo DD225 problem

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Surrey
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United Kingdom
Hi all

I joined this forum purely on basis of browing some of the threads to help me with my Megaflo problem. Hoping some of the pro's here might be kind enough to provide some input to get this resolved.

I've got a 8 yr old Megaflo DD225 cylinder which up until 2 months ago supplied hot water. I live in Croydon, Surrey and have had several local engineers attend (even those recommended by Heatrae Sadia themselves) and not one of them has successfully restored hot water.

We've had this before and switched out the thermostat which went fine (this was abt a year before current problem) but changing thermostat this time still hasn't worked, with plumber blaming dodgy valves or faulty replacement thermostat.

We're still (only) getting cold water with normal pressure and now I've become extremely wary of arranging for another so-called 'engineer' come over just to provide their opinion wihout corrctly diagnosing the problem never to be seen again!

I still don't know if problem's electrical, mechanical, dodgy thermostat or something else - I mean what is the correct procedure to replace a thermostat (assuming it's as simple as that) ie. does it involve draining the cylinder?

I'm going to try local Plumbase for a new thermostat and try to find someone to install it.

Any other suggestions greatly appreciated!

cheers guys!

Nav
 
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Are you any good with a multimeter? Before you spend out on a new stat you need to check it's the problem or your just as bad as the guys that have visited you. If you've got a copy of the installation instructions there'll be a wiring diagram in there.

Without sitting in front of the unit with a multimeter you can't say where the fault lies.

Nearly forgot, the thermostat sits in a pocket so unit doesn't need draining but confirm this is the problem before changing it.

Mike
 
All a Megaflo is is a tin bucket with two thermostats in series.

A simple way to check the thermostats prior to buying a new set is to link the two wires from the wiring centre to the Megaflo and see if the motorised valve opens and the boiler delivers heat (with HW turned on at the programmer).

It really is as simple as that, but must not be run unattended in this manner.

If you find that by linking the wires, the boiler etc starts, then you have a faulty thermostat set.

If the boiler does not start, your fault lies external to the Megaflo on the system wiring or zone valves.

If your Megaflo is 8 years old it may be the old Davtek design (Heatrae Sadia bought them in) with a separate honeywell cylinder stat and a overheat stat mounted under a cap wihich looks like an immersion heater. Linking out the thermostat is a little more awkward on these.

What you need is a local independent (ahem!).
 
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dd are direct. so only an immersion. check resistance on immersion. would guess at 8 years old it could have gone. These cylinders of this size have 2 immersions.

Are they both connected up? often only the bottom is connected. if so you could swap them over or as a temp solution wire up the top immersion.
 
cheers guys for the invaluable advice :D

Must say collective responses here been helluva lot more constructive than what I've received to date!!

Also need to correct the model is a DD145 (just checked the label left by EHV) so not large cylinder in grand scheme of things as we live in a grd floor flat.

I defo agree with SimonD that experienced independent would be best to get to root cause of problem and get it sorted though linking wires to see if motorised valves open to deliver heat could take few hrs before we detect any hot water - partly reason I believe other engineers just check electrics confirming all ok, reset the air bubble and hope it's fixed and move onto next job! Very frustrating when we've waited up to 8 hrs and, joy of joys, still cold water!!

Last engineer report claimed:
- "wrong combi and expansion valved fitted" (er, but we had no problem with hot water before!!)
- "faulty stat"

Am inclined towards believing it's stat-related problem and need to check wiring instrux and other input from swbjackson and Snd (thks for input!) so will report back.

Couple other questions for you chaps;
- am I right in thinking programmer is the copper fitting inside the stat/element enclosure?
- whereabouts will immersion be located (if applicable to DD145)?

p.s. serial number for cylinder is 14060346, element/stat 95606920.

Thanks again guys (oh and happy New Year!!)


:D :D
 
Programmer will be a timer box on the wall.

You will see a large dark grey plastic door at the bottom of the megaflo. Open this (be careful as there can be live terminals in here) and you will see the main immersion (about 3" diameter) infront of you.

Not certain on the DD145 whether you will have a second immersion higher up as a boost.
 
If it's only electrically heated you can ignore any valves or suchlike as far as resolving the lack of hot water is concerned.

If it's the unit I'm thinking of it will just have one cable running from a switch or timeswitch to a circular immersion heater in the side of the cylinder.

Just check power into the thermostat and power out of the thermostat. If it's present at both the stat is okay and you need to look at the wiring or heating element. If there's no power going into the stat it will be wiring or switch/timeswitch. It's probably worth turning the power off and checking that all the electrical connections are made properly as well.

Mike
 
Programmer will be a timer box on the wall.

You will see a large dark grey plastic door at the bottom of the megaflo. Open this (be careful as there can be live terminals in here) and you will see the main immersion (about 3" diameter) infront of you.

Not certain on the DD145 whether you will have a second immersion higher up as a boost.

I've a feeling this model is prior to the grey box ones.

Mike
 
cheers Dave

I'm sure I've missed a trick here coz there ain't no programmer and never has been - hence why I thought there was a timer type setting inside the element enclosure!! Not sure how relevant this is but whole flat is electric, ie. Economy7, storage heaters, etc.

There's just the cylinder and relevant water mains pipes, valves etc. mentioned above.

Pls correct my terminology but there's also 2 wall mounted 'switches' which I've been told are to turn power on/off to each of the elements and have never been touched...since electrics have checked out ok (I've seen the multimeter readings myself) I've thought best to leave em alone. Apart from anything else, there practically inaccessible in terms of checking internal wiring, being located where only a screwdriver with a 90 degree angle could manage! :confused:
 
Normally on E7 the bottom heater is set to come on over night and the top one is used as a boost if needed. Any chance of a picture of the setup?

Mike
 
as the water in surrey is quite hard, direct cylinders tend to to be full of scale which does shorten the life of the elements, has any one tested the elements for resistance or the fuses in your switches?
 
Completely aside from the water heating problem. The discharge pipework is incorrect. Both the PRV and T&PRV pipework should be connected in above the tundish. There should be 300mm straight pipe before the first bend on the 22mm discharge pipe, it looks like this may be short. Issues with this are that if the PRV discharges you won't necessarily know until you look at the discharge outside. Secondly if the 22mm is short of the required length to the first bend the pipe may not cope with a full bore discharge and end up spilling over inside.

Back to the water heating problem. You may find the lower immersion is wired through the same consumer unit and only comes on at night with the night store heaters. The upper immersion may well be turned off at the switch or in the main consumer unit as it is only intended as a a back up.

The thermostats should be interchangeable between the two heaters so you may be able to get yourself up and running that way.

Mike

P.S. I'd recommend that you get the discharge pipework sorted out as well.
 
Your E7 timer will be the E7 meter itself. When this clicks on the bottom immersion will be live.

The 2 switches you have are just isolators for each element.
 

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