Heating Engineers/Plumbers? - Heatrae Sadia Megaflow Pressure Question

[Toms306]

Morning all,

Not sure if this is a fault or just a 'quirk' of this system. As title I have a 'Megaflow' unvented hot water tank with immersion heater.

When I turn on any hot tap or the shower there is good pressure for about a second then it slows to a dribble for between 30-120 seconds before all hell breaks loose and full pressure is unleashed lol. I just want to know if this dribble/delay is normal for this type of system or not? There are instructions on 'resetting the airgap' on the tank but I don't want to waste the water if it won't stop the delay.

Also, as the immersion heater is using more electric than anything else in the place, is there any way I can increase it's efficiency? Would lagging the accessible pipes show a noticeable improvement?

Cheers
Tom

[bigcheez2k3]

The immersion heater just have it on at certain times and take your shower/wash up in those times.

[Toms306]

It doesn't really work like that, it heats up on with the cheap rate electric (Economy10) and is on a thermostat so it's only on for around an hour over the whole day - but that's still 3kWh!! Even the washer dryer combi doesn't use that much lol. I know it's not an efficient system, using electric to heat water never will be, but it's the only option for those of us without gas or oil.

[1616six]

Oh god, Tom is now worrying about house MPG.

[Toms306]

Oh god, Tom is now worrying about house MPG.

Lol house MPG is surprisingly interesting!! I have an energy monitor to see how much electric things are using - as I had the first 3 weeks with a broken meter before a new one was fitted lol. I'm using a lot less electric than I had estimated so far (even with the immersion heater lol) which is good. It's also 'fun' to work out when the cheap rates are to put the washing machine on and plug in chargers...

But on the other hand, I'm using a lot more water than expected. Thought that meter may have been broken as well but I recorded all the water I used over the weekend, checked the meter before and after and it was bang on! About 200 litres a day - which is apparently a third more than average, however a 5 minute shower is 40 litres, and 10 toilet flushes is 60 litres, so there's 100 already! Then cooking and washing up is another ~20 depending what's being cooked... And handwashing, shaving, teeth cleaning etc, all adds up. Haven't worked out how much water the washing machine uses yet tbf, not sure I want to know lol.

I should add I'm not actually 'worrying' about it, it costs what it costs, I'm not gonna sit in silence to save electric lol, but equally I like to save anywhere that won't impact me - such as a toilet 'frog' to save a litre per flush...

[Toms306]

Seriously no-one else uses this system!?

Well, I tried regenerating the air gap in the tank. But the pressure relief valve doesn't seem to work? Basically when you turn it, it just moves a quarter turn and 'clicks' back inwards. No water passed through the tundish as I turned it either. However there is still an intermittent drip through the tundish, possibly pointing to a reduced airgap.

On another note, possibly unrelated, I'm getting a very faint bad smell in the bathroom since yesterday, not caused by me I should add!! Theres no visible leak but most pipes are hidden and I'm convinced I can hear a drip while sitting in silence on the loo, I'm wondering if the shower tray trap is leaking (had to have kitchen plug hole and trap replaced and are same age) but its all built in and I can't see any access at all. Is there any 'radweld' style sealant that can be poured down drains to block minor leaks? If the smell persists I'll have to ask the maintenance man in but I'd rather not if its something simple.

[toseland]

actually using electric to heat water is the MOST efficient..

however, doing it in this fashion isnt.

[cully]

smell in the bathroom is probably damp from the shower tray leaking around the tray top seal i guessing your spending hours in the shower scrubbing

[Toms306]

actually using electric to heat water is the MOST efficient..

however, doing it in this fashion isnt.

Well if I had solar panels or a wind turbine maybe...

Surely a gas/oil boiler heating as and when is much more efficient?

[Paul_13]

If you're turning the relief valve and nothing is coming out there's no water getting to the heater

I could be the non return valve is faulty or the strainer is blocked.

Is the service valve feeding the heater fully open?

Tbh you shouldn't be touching any of it, unvented water heaters can cause catastrophic damage if they're done wrong.

Whole schools have been blown apart by faulty unvented water heaters

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Seriously of you don't know what you're doing with it I wouldn't be touching it.
When you saying replenishing the air gap worries me.

There is no air gap.

The expansion vessel is set to a certain pressure to maintain a constant pressure when you turn the tap on

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Also if there's no water getting to the heater chances are you've cooked it

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Can you take a picture of it to see what setup you have

[306carter]

is this in a rented property? If so just phone your landlord and they will arrange for an engineer to look at it.

[Toms306]

smell in the bathroom is probably damp from the shower tray leaking around the tray top seal i guessing your spending hours in the shower scrubbing

Not when it uses 8 litres of water a minute lol! 5 min shower in the morning, that's all.

I 'think' I've found the smell issue though, not sure why it's only now starting to smell but seems to be the basin overflow, smell seemed to get stronger after using hot water there so guessing it's breeding something in there. I haven't been using hot water there due to a faulty tap and this pressure issue but since replacing the tap headgear it is now useable so that may be why. Sprayed some cleaner/anti-bac down it and left overnight and can't smell it this morning.

If you're turning the relief valve and nothing is coming out there's no water getting to the heater

I could be the non return valve is faulty or the strainer is blocked.

Is the service valve feeding the heater fully open?

Tbh you shouldn't be touching any of it, unvented water heaters can cause catastrophic damage if they're done wrong.

Whole schools have been blown apart by faulty unvented water heaters

---

Seriously of you don't know what you're doing with it I wouldn't be touching it.
When you saying replenishing the air gap worries me.

There is no air gap.

The expansion vessel is set to a certain pressure to maintain a constant pressure when you turn the tap on

---

Also if there's no water getting to the heater chances are you've cooked it

---

Can you take a picture of it to see what setup you have

There is an air gap. I've done research into the system, I'm not just going around poking things! Water is being heated. To recap the issue, it's been intermittently dripping from the overflow/tundish since I moved in. When using any hot water there is a pressure delay of up to 2 minutes before the pressure suddenly rises to full which is inconvenient, but I want to know if that's normal for the system.

This is the system - https://www.youtube.com/watch?v=1nnpwyDpExM

This is how to regen the air-gap - https://www.youtube.com/watch?v=sKvxlQI0fH4

is this in a rented property? If so just phone your landlord and they will arrange for an engineer to look at it.

Not an engineer, just a maintenance man that tends to do the same things that I could've done in half the time and without having to wait in all day for him.

[Paul_13]

I just may know it as being something else that's all. I was a bit tired writing that response last night.

If its been dripping intermittently out of the relief valve it's either faulty or there's too much pressure building up in the cylinder

[Toms306]

I just may know it as being something else that's all. I was a bit tired writing that response last night.

If its been dripping intermittently out of the relief valve it's either faulty or there's too much pressure building up in the cylinder

Yes I agree it does seem like too much pressure, which seems to be because of a reduced air gap at the top of the tank so the water can't expand enough when being heated. But I'm not too fussed by losing a small amount of water outside, though my neighbours overflow is next to mine and his doesn't drip. But could that also cause the delay? As I can't find anything about the delay at all which either makes me think it's normal or a rare occurrence lol.

I was wondering/speculating if it could cause a vacuum effect inside the cylinder, like leaving the rad cap on when draining coolant on the car for example, until the pressure drops enough to allow the correct gap and then the water shoots out of the tap and all over the floor/wall/myself/etc... That could be complete crap though, it just makes sense in my mind lol, but as I say can't seem to find any info on that.

As for the relief valve, is it normal to just move a quarter turn and then snap back inwards or does that sound faulty? I was expecting it to have a lot of resistance and have to hold it open whilst spring pressure tried to pull it back to it's original position? Not seen a relief valve like this before as we had a different system at home - one with no pressure at all lol.

[Paul_13]

1/4 turn snap is normal.
I'm wondering if the diaphragm is f*cked

[toseland]

Hmm.. Could this be a leaking fill thingy. (Not sure what it's called, but the thing that's similar to the ball cock in a normal water tank)

I would hypothesise that this is, over a period of no use filling up past the required level then this is draining out before the fill tap is opened returning pressure after a minute or so and through

[Toms306]

Ah ok, I'll know about the quarter turn for future then!

Hope it's not the diaphragm as that's obviously something I'd have to call maintenance in for.

[Toms306]

Hmm.. Could this be a leaking fill thingy. (Not sure what it's called, but the thing that's similar to the ball cock in a normal water tank)

I would hypothesise that this is, over a period of no use filling up past the required level then this is draining out before the fill tap is opened returning pressure after a minute or so and through

This is what I originally assumed - and went into the loft looking for a tank, to find there isn't one. Hence reading up about the system which I found pretty interesting oddly! Maybe I should've done plumbing at college instead of electrics which just bores me.

I was just hoping someone else had this system (I would imagine most small purpose built flats over the last 20 years probably do!) or happened to be a Megaflo installer to see whether they had the same delay or not. As I say the occasional drip doesn't bother me too much, looking at the lichen growth under the outside overflow it's been dripping long before I moved in lol. But this delay is really quite inconvenient so I can't see it being normal.

[cully]

the delay is due to the incoming water pressure being below the cylinder pressure i believe

[Toms306]

So it would be normal for this system then?

[Paul_13]

Cully, that's the case any way, that's how they work.

Incoming main will be say 5bar > this then goes through a pressure reducer to bring it down to 3 bar.

The water passes through a non return valve which traps the water in the cylinder.

The water is then heated and the pressure will rise in the cylinder by around a bar

Of the pressure goes over 5 bar the relief valve sets off and Lets pressure out before the cylinder turns into a bomb.

The air pocket in the diaphragm is compressed when the water is pressurised and this allows the water pressure to be maintained when water is drawn off.


Now if there's no pressure then loads of pressure my guess is the diaphragm is f*cked and is not maintaining the constant pressure straight away and then the diaphragm frees off hence the burst of pressure

[cully]

are you sure there is a diaphram in this system im sure its just an air pocket at the top not a rubber bag like the expansion vesals

hence why it needs recharging via the taps and the safety temp/pressure tundis vent and not via a shrader car type valve nipple

[Paul_13]

Or the non return valve is sticking shut and the pressure difference is freeing it off

[Eeyore]

put a brick or two in the toilet tom. Thatll save you water

[Toms306]

put a brick or two in the toilet tom. Thatll save you water

And damage the syphon membrane with bits of grit falling off it lol... Much better to use a bottle of water in there OR with Anglian Water we can get free toilet 'frogs' which save a litre per flush on a 7 litre cistern.

When I average 10 flushes a day that means I'm getting just over 1 free flush per day. Its the shower that uses the most though...5 mins in the shower is the same as washing the car twice!!

[Kezzieboy]

You can get restrictors for showers to limit the flow.

[procta]

tom I bet you have bust it

[toseland]

put a brick or two in the toilet tom. Thatll save you water

And damage the syphon membrane with bits of grit falling off it lol...  Much better to use a bottle of water in there OR with Anglian Water we can get free toilet 'frogs' which save a litre per flush on a 7 litre cistern.

When I average 10 flushes a day that means I'm getting just over 1 free flush per day.  Its the shower that uses the most though...5 mins in the shower is the same as washing the car twice!!

so tie the brick in a bag!

[Toms306]

You can get restrictors for showers to limit the flow.

Yep, got one of those free too!! It's terrible though - only saves 2 litres on a 5 minute shower (15 seconds worth) but takes more than an extra 15 seconds to remove the soap/shampoo with the restricted flow! Will be removing that straight away lol.

put a brick or two in the toilet tom. Thatll save you water

And damage the syphon membrane with bits of grit falling off it lol...  Much better to use a bottle of water in there OR with Anglian Water we can get free toilet 'frogs' which save a litre per flush on a 7 litre cistern.

When I average 10 flushes a day that means I'm getting just over 1 free flush per day.  Its the shower that uses the most though...5 mins in the shower is the same as washing the car twice!!

so tie the brick in a bag!

But as I've already said, Anglian Water send out free things to do the same job with less hassle...

[bigcheez2k3]

I'd rather have a decent shower than give a shit how much water it uses.