megaflow problem - ideas please....

[megaflow]

hi all, looking for some help before I launch a megaflow! I have a Ideal Classic boiler and a Heatrae Sadia megaflow tank. In order to get hot water the central heating has to be on. It was installed when the house was built about 4 years ago and has never worked. The plumbing firm who installed it refused to look at it as they fell out with the builder who went bankrupt! British Gas did aa survey on it and decided that it had been piped up incorrectly so my mate (plumber) had a look and said it was 100% correct though thought that the return for water was a bit close to return for heating (or something like that so he changed the location of the tee...?! It seemed to work okay but 24 hours later it was back to it's old tricks. If you switch just the water on, the zone valve opens and the boiler fires but goes back off again after a few seconds. In the installation manual it recommends an air valve be fitted near the HW return but there isn't one - could this be the fault?

Please help......

 

[sonray ltd]

im bit confused why doesn't your plumber fix it as he can see the job we can't ?
or does he not hold a g3 cert to work on it ?

as for your problem it sounds like the water isn't circulating if the boiler cut off.

is the flow pipe to the cylinder hot ?
is the valve staying open when boiler cuts out to say it is still calling for heat ?
is the return pipe cold/hot ?

sounds like an airlocked coil.

 

[megaflow]

im bit confused why doesn't your plumber fix it as he can see the job we can't ?
or does he not hold a g3 cert to work on it ?

as for your problem it sounds like the water isn't circulating if the boiler cut off.

is the flow pipe to the cylinder hot ?
is the valve staying open when boiler cuts out to say it is still calling for heat ?
is the return pipe cold/hot ?

sounds like an airlocked coil.

He hasn't got his unvented ticket! Flow pipe to cylinder is hot but only when the heating is on and the valve does stay open when boiler cuts out - and pump runs too. The return pipe is cold!

 

[sonray ltd]

you say flow pipe is hot only when heating is on - is this because the boiler is cutting out to quick when hw only on and the heat is not reaching the cylinder.

have you tried turning everything off so nothing calling for heat and the hw zone valve closed and bleeding the hw flow pipe into the coil.

if their is not a bleed valve on the flow pipe between the zone valve and cylinder place a towel or bowl under the zone valve and slacken the nut to release any air in the coil. zone valve must be closed.

 

[megaflow]

you say flow pipe is hot only when heating is on - is this because the boiler is cutting out to quick when hw only on and the heat is not reaching the cylinder.

have you tried turning everything off so nothing calling for heat and the hw zone valve closed and bleeding the hw flow pipe into the coil.

if their is not a bleed valve on the flow pipe between the zone valve and cylinder place a towel or bowl under the zone valve and slacken the nut to release any air in the coil. zone valve must be closed.

I guess so - to be honest the whole thing baffles me - i'm a kitchen fitter and tend to stick to wood - my plumber does all my gas work and he is a central heating engineer - he says he's too old to bother learning about this sort of system so doesn't really understand it...

I'll try bleeding it from the zone valve - is that why there should be a bottle vent near there?

Appreciate you help!

 

[sonray ltd]

any bleed vent.

if he's a heating engineer these cylinders are no different to any cylinder but only use mains water and not gravity.
he can work on your problem as he is only not allow to touch any of the pressure valves etc, he is working on the heating side of things not the unvented dhw

 

[megaflow]

any bleed vent.

if he's a heating engineer these cylinders are no different to any cylinder but only use mains water and not gravity.
he can work on your problem as he is only not allow to touch any of the pressure valves etc, he is working on the heating side of things not the unvented dhw

I reckon he falls in to the bracket of nothing new is good - he's a vulcan devotee!

Just tried bleeding it from the zone valve nut and only water came out - how long should I bleed it for before any air is vacated?

 

[sonray ltd]

depends how far down the airlock may be.
if you have had the heating on etc you could do it until the return pipe gets hot water through it.

 

[megaflow]

depends how far down the airlock may be.
if you have had the heating on etc you could do it until the return pipe gets hot water through it.

righty-o, i'll try again once the kids have had a bath - thanks again!

oh, any other ideas if it's not air?

 

[sonray ltd]

i just re read your post you are getting hw when the heating/hw is on yes ?

 

[megaflow]

i just re read your post you are getting hw when the heating/hw is on yes ?

sure am

 

[sonray ltd]

put hw only on and check if the pump is running.

i know it runs with heating or heating/hw but check with hw only

so zone valve opens boiler fires but does pump run as well ?

 

[megaflow]

put hw only on and check if the pump is running.

i know it runs with heating or heating/hw but check with hw only

so zone valve opens boiler fires but does pump run as well ?

With only hw on the pump runs, zone valve opens, and boiler fires then switches off after a short time, even if hw tank is cold...

 

[sonray ltd]

thats strange as it proves no blockage or air as it circulates ok with heating/hw on but not just hw.

 

[megaflow]

thats strange as it proves no blockage or air as it circulates ok with heating/hw on but not just hw.

foxed ya! it must be something really stupidly simple?

I take it the immersion doesn't need to be on?

 

[sonray ltd]

no not with the boiler heating it. only if the boiler breaks down etc as a back up.

have you any pics of the cylinder set up etc ?

 

[megaflow]

no not with the boiler heating it. only if the boiler breaks down etc as a back up.

have you any pics of the cylinder set up etc ?

No but I could take some - have to empty the cupboard as its chocka with airing clothes! In fact, it's so compact in there and most of the pipes like the one with the strange named thing beginning with a T are towards the rear of the cylinder... My guy has had all the floor boards up and traced all the pipework though and its correct in accordance with installation guide. Will try though if it helps - how do I upload them on to the thread?

 

[sonray ltd]

i use photobucket for pics.

put photobucket in google etc.

 

[megaflow]

just tried to upload pics but they are too big for this site - can I pm them to you?

 

[sonray ltd]

yes if you want.

 

[megaflow]

I thought i'd be able to cut and paste a picture on to a pm but can't - technology is never simple!

 

[sonray ltd]

when the hw on and the boiler kicks in then the boiler cuts out the zone valve stays open is the pump still running ?

 

[megaflow]

Yep, pump still running...

 

[sonray ltd]

well at the moment i can't see any reason for the boiler to shut down, if the cylinder is still calling for heat, valve still open, pump still running.

does the boiler never cut back in if you leave it once its gone off with all the above still calling for heat ?

 

[megaflow]

It only fires again if the room thermostat kicks in and the boiler starts to cook the CH but if only HW is on the control panel then the pump just whirs away and the boiler stays dead. It really has baffled me and i'm at the stage now with it where i'm considering just taking it out and getting a combi fitted. I'm sure that's not necessary though, it's just a case of finding the fault but that seems to be like the proverbial needle in the haystack!