What has gone wrong with my unvented system?

[dpm_dpmartin]

Hi all - I'm hoping someone here could provide me with a bit of insight, advice and guidance as to what might have gone wrong with my home hot water system (central heating remains fine).

The system was last serviced in Feb 2017 but - at the moment - the system is not producing hot water by using gas... that's by the timer or if I press the Water - Extra Hour button on the programmer (you can see it on the wall to the right) - the red light does come on, but the boiler does not kick-in (my Nests do not control hot water, just CH).

The guy who looks after the system is aware of my issue, but he's said that he can't get out to me until between Christmas and New Year so I have resorted to the back-up - the 2 immersion heaters for my hot water.

They certainly work, but I've ran into a secondary problem. If I leave the immersions (or just the lower one) on for a prolonged period of time then, after a while a trickle of water will start to come out of that pipe, after much more time it'll become a flow of water that escapes outside.

Now, I know that means something is wrong - but I don't know what. I bought this house in 2014 (with the system working fine) and for the first 2 years (completely unbeknownst to me, admittedly) it was heating water by running off the 2 immersions heaters all the time, they were switched on constantly and the Hot Water at the Programmer was in the OFF position. It was only in 2016 when a Central Heating Engineer recommended I turn them both off and use the boiler to heat my hot water.

Since then I have not had the immersions switched on and I've never had water escape from that pipe. Now that the boiler's not heating the hot water (problem #1, I guess) and I'm using the immersion heaters I suddenly get water coming out of that pipe (problem #2) again.

It's actually problem #2 that I'm most curious about - why is that happening? What is at fault? Is the immersion heater not cutting-out when it should? Is there something wrong with the pipework that has degraded over time (as nothing has been changed)? Or is there a failure in that 35 litre header tank?

I'm asking here because I'd like to stop that happening if I can. However, if I'm going to be told I need a new part then I can prepare for the cost as well.

Hopefully this picture is helpful? I am at home so I can take pictures of anything here...

 

[dpm_dpmartin]

No idea why the image is not showing, it does in Forum Preview - will try again...

Still didn't work - direct link http://www.hmusiccentre.org.uk/forumimages/boiler-01.jpg

 

[terryplumb]

The tundish ,where water is running / dripping ,is part of the safety system.and it is allowing excess pressure out . various things can cause this and you should not attempt to do anything yourself ,but call in a G3 engineer ,ASAP.

 

[dpm_dpmartin]

That's OK - I have him ready to attend (but not until after Christmas, for now I'm manually turning on the immersion and then turning it off after a while - I can't leave it on unattended otherwise water will go out of that tundish). I'm really just wondering why the excess pressure is being created (obviously because water is being heated) now, when it wasn't for years before. Some part of the overall system has either failed or isn't working as it used to, but what? Various things is what I thought...

 

[aptsys]

If there is a continuous discharge of water, it could indicate the thermostat on the immersion heater has failed. It's doubtful both have failed, so in the meantime you could try just turning one on to identify which is faulty.

 

[terryplumb]

When water is heated it expands , in a sealed pressurised system as yours ,this expansion is accommodated in the expansion vessel. The hotter the water ,the greater the expansion and increased pressure. If there is a failure to accommodate this ,a pressure release valve opens and allows water / pressure drop via the tundish and its pipework. This is the case whether heated by boiler or immersion heaters.so you have a number of issues. 1 the boiler / system components / controls are not giving you domestic hot water. 2 ,your back up immersion heaters are giving you hot water ,but at what temperature I don't know .maybe temps are normal for all I know ,and its just an expansion control problem. Or temps are excessive thru temp control stats failure and water getting to boiling point. Without being there its just a guess. If I were you I wouldn't wait till after Xmas I would act now. There are other options besides your guy who can't get to you for weeks.regards terry

 

[dpm_dpmartin]

If there is a continuous discharge of water, it could indicate the thermostat on the immersion heater has failed. It's doubtful both have failed, so in the meantime you could try just turning one on to identify which is faulty.

Good input. I had already tried that... the results were that I get discharge if both are on, or if one is on. If both are on, I've seen it shoot out at some speed, gurgling away (that was the day I could hear it from my Study inside the boiler cupboard with the door shut)... when I tried just the bottom one it did still dribble out, but I turned it off before seeing if it got just as bad (I did expect it to).

I keep the boiler cupboard door open now while I'm heating water to have a shower... there's a lack of trust between us.

 

[dpm_dpmartin]

If I were you I wouldn't wait till after Xmas I would act now. There are other options besides your guy who can't get to you for weeks.regards terry

Yes, I know - I'm tempted... it's just that he did the Service back in February, so I know that he's familiar with the system - I also have faith that he'll not rip me off. I know it's not special, but I have had some people (I mean Central Heating Engineers) looking at it and going "urrh?"

 

[dpm_dpmartin]

When water is heated it expands , in a sealed pressurised system as yours ,this expansion is accommodated in the expansion vessel. The hotter the water ,the greater the expansion and increased pressure. If there is a failure to accommodate this ,a pressure release valve opens and allows water / pressure drop via the tundish and its pipework. This is the case whether heated by boiler or immersion heaters.so you have a number of issues. 1 the boiler / system components / controls are not giving you domestic hot water. 2 ,your back up immersion heaters are giving you hot water ,but at what temperature I don't know .maybe temps are normal for all I know ,and its just an expansion control problem. Or temps are excessive thru temp control stats failure and water getting to boiling point.

Thank you for this. I can confirm water never came out of the tundish when the water was being heated by gas, only when being heated by electricity. It was why I thought some kind of auto-cut-off failure on the immersion - just as was postulated. I guess I'm as in the dark as I was before. My guy has asked me for details of that expansion vessel so he can price up. However, still the issue as to why the boiler ain't doing its thing.

Although, I admit I preferred the system when I was heating hot water via the immersions. I didn't notice any difference in my bills and it was a lot quieter for me.

 

[stem]

We had the same fault twice at work, but with different causes. The first time, the pressure vessel was faulty. I was told that the internal rubber membrane that kept the air separate from the water had split so the whole vessel filled up with water. Then as the water heated and expanded there was no air pocket left for it to compress and so it exited via the pressure relief. Maybe it's possible that the immersion has heated it to a higher temperature and caused more expansion which has split it.

On the second occasion the pressure relief failed and so water discharged from it. But as terryplumb stated neither are a DIY job.

 

[terryplumb]

With so much water being evacuated have you had to re pressurise ? Given the fact that its been " serviced " regularly and in Feb ,I would raise the question why are you experiencing such issues ? Pressurised systems require a qualified G3 certified engineer to work on them. Not all are ,hence the head scratching !!!

 

[dpm_dpmartin]

But as terryplumb stated neither are a DIY job.

100% agreed. I'm just wanting to understand more... so at least I can hold a conversation about it.

 

[stem]

Yes same with me, I got the G3 guy in and asked him questions so I could understand what the problem was. Helps to understand for next time

 

[dpm_dpmartin]

With so much water being evacuated have you had to re pressurise ? Given the fact that its been " serviced " regularly and in Feb ,I would raise the question why are you experiencing such issues ? Pressurised systems require a qualified G3 certified engineer to work on them. Not all are ,hence the head scratching !!!

I did turn that black lever underneath the boiler, to the right-side of my picture, a week or so ago... but not because it told me I had to or anything like that - the boiler display is quite laconic - just because I realised I was getting no hot water from the boiler and thought I'd give it a go... so it went up to about 1.8 on the day. Now it's at 1.4 (in my picture earlier today) to 1.6 (right now).

 

[St0rmer66]

I did turn that black lever underneath the boiler, to the right-side of my picture, a week or so ago... but not because it told me I had to or anything like that - the boiler display is quite laconic - just because I realised I was getting no hot water from the boiler and thought I'd give it a go... so it went up to about 1.8 on the day. Now it's at 1.4 (in my picture earlier today) to 1.6 (right now).

That's the pressure in the boiler and heating system, not the cylinder. Totally separate.