Megaflow running out of hot water

[Sam53]

Hi

Have a 3 year old 300l Heatrae Sadia Megaflow (connected to a Worcester 24SBi) and it seems to be running cold very quickly compared to the number of hours the DHW is set to heat for.

Ive set the timer to heat for DHW from 3am to midday and then from 17.15 to midnight (as its in a tenanted property of 6 people) but it always seems to run cold quite quickly in the morning around 6.30am and in the evenings around 8pm. Its been working well without complaint up until about 3 weeks ago and ive had the guy who installed it to come check it out. He said there was nothing wrong with it and just increased the hours on the boiler timer to heat DHW for longer periods. All seemed well for the first few days but then its back to the same problem. Its quite confusing as the problem doesnt seem to be consistant every day......but on every other day or so. I doubt if its the 300l water tank emptying out so quick due to lots of usage (long showers etc) as ive had the same tenants in the house for a while now without any complaints (up until 3 weeks ago when the problem started).

I went out last night to check it myself when it began to run cold again and the only thing that comes to mind is that when the radiator heating switched off (as per the timer settings), the hot water tap began to run warmer and eventually hotter after about 10 to 15 minutes. Could the rads be taking up all the hot water as its also timed to come on (and off) within the on (and off) timings for DHW?

I'd really appreciate any advise as to what to do or get checked out as its quite baffling because the problem is not constant everyday.

Many Thanks!

 

[gas4you]

You need to check the operation of the 2 port valve (and 3 port if fitted as well) to check the system water is getting to the megaflo coil.

Have you checked for air on the bleed valve on the indirect return out of the megaflo? next to the cylinder.

 

[Sam53]

Hi Dave

Many thanks for the quick reply......i'll get the plumber to take a look at what you've suggested (as i dont have a clue).

Could it be anything else (if they all work fine)?

Has anybody else had experience with troubleshooting similar problems on a megaflow system?

Many Thanks!

 

[corgiman]

dont forget to check to see if you need to re do the air bubble, this can play silly beggars with hot water capacity too

there is a sticker on the side of the thing telling you how to do it

 

[Sam53]

Thanks guys for the suggestions but the plumber has been in and said he can't find no fault(s).

So im really confused as what to do now.

He suggested leaving the DHW (at the timer) on 24hrs. Would this shoot my gas bill through the roof?

Also he suggested to switch the heating off for the 2 hour window in which people usually take their showers at.......so to divert ALL the hot water to the taps (rather than the demand through the rads). Does this make sense?

Any other suggestions?

Cheers!

 

[corgiman]

is you plumber G3 quailified?

if not call heatrae sadia and ask for one of their approved engineers to visit you

 

[gas4you]

Sounds like your plumber is an idiot to me

 

[croydoncorgi]

Another thing to check is whether there's a 'hot loop' with a pump which re-circulates water around the DHW pipework and back to the cylinder, to ensure that the taps run hot quickly. (Without circulation, the water in the pipes cools down and the tap has to be run for a long time before the user gets any hot water.)

AFAIR, Megaflos tend NOT to have a 'secondary tapping' for the Return connection near the top of the cylinder. (Perhaps thoughtless) plumbers then connect the Return to the cold inlet at the bottom of the cylinder. Unfortunately, this has the effect of turning the complete contents of the cylinder tepid as soon as the heat goes off. The reason is that the warm water entering the bottom of the tank tends to rise upwards (due to convection) and causes mixing of the entire contents.

A partial answer is to fit a pipestat on the Return and wire it into the pump circuit, so that the pump does not run continuously - only when the water in the pipes has cooled down.

If the DHW pipework in the building is not properly insulated - you have a problem!

 

[Sam53]

Seems like its not quite my month!

Now the boiler (Worcester Bosche 24sbi) has packed in.........it wont fire up either from the re-ignition button or when the system is switched off at the mains and then turned back on. (The green light comes on but nothing else). So now i have no hot water and no CH.

Can anyone recommend me a engineer local to Ealing , W13 (West London) who has experience on both the 24sbi and the megaflow.

Many Thanks!

 

[corgigazza]

Chances are it will be the pcb packed up, try the corgi web site for someone in your area