What is causing water to come from overflow pipe

[Paul Langley]

Hi everyone,
I am new to this site so I hope I am posting on the correct forum. I just bought a house with u8nderfloor heating serviced with a Vaillant Echotec plus boiler. It is a pressurised system (no tanks in the loft) but it has a stainless hot water cylinder so it is not a combi boiler heating hot water direct from the mains. The house was built 11 years ago so I guess everything is that old. As background, I have just replaced a faulty pressure vessel in the boiler (I was slowly losing pressure and water came out when I checked the shraeder valve) and that problem now seems solved. I am a competent DIYer and not a plumber by trade though I did install a complete central heating system in my previous house.
The problem I have is about 0.5 litres of water comes out of an outside overflow pipe when the shower is used and is running for 5 minutes or so. As I did not have the house built and the majority of the pipework is underfloor or boxed in, I am uncertain where the source of the overflow pipe is. Anyone got any ideas as to what the problem is likely to be. I suspect the overflow pipe also discharges water if a hot tap in a sink is left running for several minutes but I have not yet checked this.
When hot water is drawn off from the system and cold water from the mains replenishes it, I am guessing there is some sort of pressure increase that may activate a pressure release valve somewhere in the system but this is only a guess. Any ideas and help will be greatly appreciated and thanks in advance to anyone who can help

 

[SimonG]

get a g3 unvented registered engineer

 

[Riley]

And you should not be replacing the expansion vessel in your boiler as the cover forms a combustion seal.

I would say likelihood is that your shower mixer is passing and forcing water back up into your loft tank causing it to overflow

 

[SimonG]

And you should not be replacing the expansion vessel in your boiler as the cover forms a combustion seal.

I would say likelihood is that your shower mixer is passing and forcing water back up into your loft tank causing it to overflow

Took as unvented hot water.

 

[Riley]

G3 is technically vented too

 

[SimonG]

G3 is technically vented too

smart rs

 

[Riley]

Well I was backing you up you could’ve got away with it if it wasn’t for those pesky kids

 

[Burger]

Do you know it’s definitely an overflow pipe? You said you don’t know where the source is, do you mean where it’s located or what’s causing it?

Could be as Riley said, mixer passing.

 

[Paul Langley]

CBW1982 - pretty sure it must be some sort of overflow pipe. It is a 15mm copper pipe boxed in on the inside of the house, exiting the exterior wall about 800mm above outside ground level with an elbow and 300mm of vertical 15mm copper pipe. I assume therefore it is to discharge something outside if there is a fault. The problem is it is not easy to trace where it comes from.
Rily - Can you expand on your first paragraph as to why I should not change a defective expansion vessel?
Thanks Paul

 

[Riley]

I gave you the reasoning. If it’s in the boiler you can’t touch it legally. If it’s on an unvented cylinder you can’t touch it legally. Give us a pic of the overflow

 

[Paul Langley]

Riley - I now understand that what you are saying is it is illegal for me to do it. Useful info for me as I have just returned from living abroad for over 30 years and was not aware of this regulation. Thanks

 

[Paul Langley]

Riley - Sorry; missed off the bit about the pic. It would only be a pick of a brick wall with a bit of vertical 15mm copper pipe venting into the open air outside the house.

 

[Riley]

Ok but ignorance is no excuse my friend. It’s been illegal for some years for unqualified or non competent persons to work on gas appliances. I would recommend a gas engineer visit to check that the seals have been replaced correctly to prevent risk to you and your family. Whilst there they may be able to advise on your overflow problem.

 

[Riley]

Riley - Sorry; missed off the bit about the pic. It would only be a pick of a brick wall with a bit of vertical 15mm copper pipe venting into the open air outside the house.

Is the boiler on the other side of the wall?? Are you often topping up pressure on your system? Or is it a vented system?

 

[Paul Langley]

Riley - The boiler is, in fact, on the first floor landing with the hot water cylinder and associated pipework etc. Before the boiler expansion vessel was changed, the system lost pressure over a couple of weeks and needed topping up to prevent the boiler going into fault mode. Since the expansion vessel was replaced, the system now maintains pressure and no longer needs topping up.

 

[Riley]

Can we get a pic of your cylinder please

 

[Paul Langley]

Riley - I'll take a picture tomorrow and post it if I can find out how I do that on this forum. In the meantime, if it helps it is a Kingspan Range Tribune HE stainless cylinder. The secondary flow and return are not used and are capped off. The central heating system was designed by Nu- Heat who are bound to be known to you I suspect.

 

[Riley]

Unvented cylinder. Based on description. Sorry @SimonG was right. Doh.

I think you have an underlying problem here which again sadly you are not qualified to work on. You require an engineer with G3 ticket

 

[Paul Langley]

Riley - Thanks for everything. Not easy here on the Isle of Wight. Only been here a short while. Emailed the gas engineer whose sticker was on the boiler as the company who serviced it in the past together with one other I got from the internet. That was over two weeks ago and I am still awaiting a response! Maybe a member who has a G3 ticket an who is on the island will see this post; here's hoping!

 

[Riley]

Take a look on the gas safe site. Many engineers on. There hold G3

 

[Paul Langley]

Thanks Riley; will do and hopefully I will find someone on the island who wants a job.

 

[John.g]

Doesn't the unvented hot water cylinder have a E.vessel and a TPRV?.

 

[Riley]

Yes but can’t be worked on by op

 

[John.g]

Agreed, but surely he can look at the tundish and see if the TPRV is discharging water, for whatever reason.

 

[SimonG]

if its piped correctly. which from the description it possibly isnt

 

[Paul Langley]

Thanks to all who have commented; much appreciated. It appears from Riley's latest comment, I am not permitted to do any work on the domestic hot water system? In an effort to give as much info as possible to a heating engineer, I this morning ascertained that the white EV on the hot water system has no pressure in it whatsoever though no water exits the schrader valve indicating to me that the diaphragm is probably intact. I assume from all said above, I am not permitted to depressurise the hot water system and recharge the EV to check if it is sound?

 

[Riley]

No you need to be G3 to work on an unvented hot water system. In addition it sounds like it’s not piped correctly so you really need to get a pro tohave a look

 

[Paul Langley]

Thanks Riley. Will do. End of thread from my end.

 

[Riley]

No worries fella we don’t mean to be awkward but safety is our paramount concern

 

[Paul Langley]

I appreciate that safety is your paramount concern and I echo that. If you turn out to be correct and the system is not piped correctly, it is a pity that Nu-Heat who designed the system (if the design is faulty) or the installer who may not have followed Nu-Heat's design, do not have the same view about safety as you and I.

 

[Riley]

Very hard to say without seeing but if the discharge is run in 15mm it ain’t right

 

[John.g]

Even if it is piped perfectly then the TPRV will discharge water every time the cylinder heats as there is no place for the expansion volume to go in the event of a punctured E.vessel bladder or no airend air (as in this case) except that it can expand back through the cold feed?

 

[Paul Langley]

Riley - Noted and thanks. John.g - I suspect you may have hit the nail on the head. I imagine, from what has been said, that if I either turn off the boiler and let the DHW go cold or draw off a significant amount of hot water and then let the boiler reheat the cool/cold cylinder, I should see signs in the tundish of water discharging from theTPRV as the water in the cylinder expands and has nowhere to go as the airless EV is not functioning?

 

[SJB060685]

When the water is heated and there is no room for expansion (for whatever reason) then the 6bar expansion relief valve will discharge through D1 to tundish and then through D2 and out. Water should not expand back into the system through the double check valve

 

[Riley]

Hi Paul I’m going to have to stop it there mate as you are fishing for info we will not give. Sorry my friend please take the advice given before and get an engineer in with the relevant qualifications.