Problems with unvented hot water suystem

[vics99]

Hello

As a complete ignoramus when it comes to plumbing, I’m hoping that the experts on this forum will be able to help me.

Our house has a Megaflo unvented hot water system. It has been here for 20 years, since the house was built, and has always worked well.

About 6 months ago we had a new condensing boiler fitted by a very well known company. Since then, we have had two problems:

-- when you turn on a hot tap anywhere in the house, the water takes much longer than before to run hot. (I wouldn’t have thought that just replacing a boiler could have had this effect, but it has.)

-- often when first turning on the shower (which is in its own cubicle), and sometimes when turning on a hot tap, we get a very loud resonance noise from the airing cupboard where the hot water tank is located. It’s rather like the noise made by a passing vehicle or overhead plane, but loud enough to fill the whole house. If you leave the shower running, the noise swells up, stays very loud for perhaps 30 seconds and then gradually dies away.

After a complaint to the well-known company, an engineer came to investigate. But on that day we just couldn’t get the noise to happen, despite turning the shower on and off repeatedly. And he didn’t seem interested in the slow-running hot water. So he said that there was nothing he could do. Since then, of course, the noise has been there almost every morning.

It’s probably worth mentioning that, besides changing the boiler, the installers also fitted what they said was a safety by-pass pipe in the airing cupboard. As they explained it, this is to cover a fault condition where a main valve is closed but the pump is still running. In this case, the water flows round the safety by-pass pipe.

The two photos show the plumbing in the airing cupboard. The new safety by-pass pipe is the one with the valve that has the red cap. That pipe always seems very hot, which strikes me as a bit strange.

If anyone could offer any advice, it would be much appreciated.

Thanks.

Vic

Untitled

• vics99
• 10 Mar 2014
• 1

Untitled

• vics99
• 10 Mar 2014
• 1

 

[oldbuffer]

Could you:

a. Let us know what the old boiler was.
b. Let us know what the new boiler is.
c. Provide a picture of the pipework into / out of the top of the MegaFlow.

When the noise occurs, can you feel any of the pipes in the airing cupboard vibrate, and if so which one(s)?

Of the pipes going to / coming from the auto bypass valve, which is getting hot, the upper, the lower or both?

 

[vics99]

Hi Oldbuffer

Thanks for taking an interest.

The old boiler was a Potterton Netaheat Profile 60e. The new one is a Worcester Greenstar 15Ri.

At the top of the boiler there’s just a single pipe coming out of the centre. Please see the new photo below.

Although the noise is definitely coming from the airing cupboard, it’s very difficult to narrow down further than that. The whole arrangement just seems to emit this very loud noise. I haven’t been able to feel any of the pipes vibrating. Next time it happens – probably tomorrow – I’ll check again.

The new pipe is very hot both above and below the auto bypass valve.

Curiously, the pipe coming out of the top of the Megaflo is usually cold, though it does sometimes get hot. I would have expected it to be hot all the time. (We keep our hot water on throughout the day.)

That’s it for the moment. Thanks again.

Vic

Untitled

• vics99
• 10 Mar 2014
• 1

 

[oldbuffer]

I think you'll need to get someone in to sort it out. Whoever you get should have "G3" certification if he / she is to work on the MegaFlow.

My initial thought was that a combi might have been installed, and the hot water circuit connected direct to the combi. This is not the case.

I think you need to separate the problems.

a. Long wait for hot water. Its possible (but unlikely) that you have a hot water system with a secondary return. Such systems circulate hot water continuously with a (special) pump so there is little or no delay in getting hot water out of a tap. These usually run off a timer. If you had one and it has not been reconnected or been turned off that would account for the delay. However there are a number of other possibilities which would require a diagnostic visit to review.

b. The noise. Again there a a good number of possibilities, including unclipped pipework, the need to recharge the expansion gap in the cylinder, and / or the air side pressure in the white expansion vessel (top left of picture 3). Consider making a recording of the noise (smart phone?) so that an engineer can hear what it sounds like, even if it doesn't occur during a visit.

c. The hot bypass pipe. This suggests that either it has not been adjusted to the correct setting, or there is a blockage on either or both the heating and CH circuits causing the bypass to operate. Its possible the motorised valve for the MegaFlow has not been wired correctly, but again it needs on-site investigation and testing.

As you say, changing the boiler should not have affected the hot water. You might wish to consider putting the problem in writing to the boiler installer, and suggesting that if you have to get some other firm to fix the issues, then you will be asking the boiler installing company to pay the bill if it proves to be an installation fault. But don't hold you breath.[/b]

 

[vics99]

Thanks Oldbuffer.

I'll do as you suggest and make a recording and then get the engineer back out. Hopefully they'll take the problems more seriously and make some attempt to fix them.

Thanks for all your help.

Vic

 

[Agile]

Unless he can repeatedly hear the noise then it would be very difficult for him to identify the cause!

Is this noise JUST when you take hot water?

Tony

 

[vics99]

Hi Tony

Yes, it's just when we use hot water.

Specifically, we have a downstairs shower room where the shower is in a cubicle (i.e. it's not just over a bath), and the noise normally comes when my wife turns on that shower in the morning. It seems to occur when she turns the shower to full and over the weeks she has become adept at turning it on more slowly, shutting it down if the noise starts and then trying again. Trouble is, it happens pretty much every morning and she always needs three or four attempts.

Also, our bedroom has an en-suite and the noise has happened a couple of times when we've turned on the basin hot tap.

Those have been the only two causes. It doesn't happen, for instance, when we turn on the hot tap at the kitchen sink.

Thanks for your help.

Vic

 

[Agile]

Has anyone checked the pressure in the expansion vessel?

Tony

 

[vics99]

Hi Tony

Not to my knowledge. I don't know what they did during installation, but the engineer who came out after we reported the problems didn't seem too interested. He said "I'll try twiddling the valve on the by-pass pipe" but then just said "ooh that's hot" and left it alone.

Vic

 

[jeff the gasman]

Cold be the pressure reducing valve vibrating on its seating and also I have known the flexible pipe to expansion vessel to cause similar noise.
PITA sometimes!

 

[jeff the gasman]

By the way the pressure reducing valve may also provide a balanced supply to showers etc. if you have had a shower fitted at the same time this could be the problem. Cold water at high pressure can leach through the shower and cause hot water delay.
Hope this helps.

 

[vics99]

Thanks Jeff. I'm afraid my ignorance is going to show:

1. Which is the pressure reducing valve? Is it the one on the safety by-pass pipe. That's the only bit of the plumbing that was changed when they fitted the new boiler.

2. Sorry, I don't know what PITA means.

3. The shower has been there since the house was built, 20 years ago. These problems only started when the new boiler was installed, 4 months ago. So I've never suspected the shower.

Vic

 

[Dan Robinson]

Pita is "pain in the a7se"


Could be the pressure reducing valve.

Could be incorrect charge in the expansion vessel.

Could be an inadvertently knocked loose pipe (the only thing likely to have been caused by the boiler install).

Either way it need a professional visit.

 

[vics99]

Thanks Dan. Trouble is, after I complained, the well-known company sent out one of their engineer's. And - Sod's Law - that was about the only day when the hot water system didn't make the noise. So basically (and understandably) he said there was nothing he could do.

I'm just trying to get a bit more understanding of what the problems might be before calling them out again. Knowing my luck, we'll get another day when the noise just doesn't happen.

 

[Agile]

Exactly!

He does need to see it malfunctioning.

Strangely, you have been told by engineers and also even on this forum of aspects relating to the heating like the auto bypass valve which are not related to your problem which is solely concerned with hot water delivery.

Tony