Warm water from cold taps unvented cylinder

HI, i haven't come across the potential issue of the cross over of the mixer valves or what that means so apologies but the inlet group has already been changed once to try in case that was causing the probem. THe plumber said there was slight limescale build up (we are in a hard water area but it has only been set up for 6 months) but we had exactly the same issue one it had been replaced so assume the inlet group is all fine.

I have felt all pipes in a morning for goodness knows how long to try and identify what is happening.

I'm not sure if you have seen the photos but there is one pipe going in to the combination valve (which i assume is the cold supply) and then another coming out of the back (which i assume is the balanced cold). I have held both of those pipes when a tap is turned on and I haven't felt a glug of hot go through but you don't feel the freezing cold water going through them straight away. They remain a tepid temperature before they go really cold

However, i have then just tried them and the same pipes are currently pretty cold, i then turn the cold tap on the the same pipes get even colder but there was still a bit of warm coming out of the taps. However, the long cold inlet pipe to the cylinder is still pretty cold and did not change temperature when the cold tap was turned on.
 
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Can you isolate your HW supply? By doing so, you should get no water from a HW tap (once the residual water in the pipe has drained out). If you do, a mixer valve somewhere may be allowing cold and hot to mix (usually debris holding the NRV open).
 
I can't stop puzzling this one. Here are my final thoughts...

Taking note of the professionals' comments and what you have said, we can probably assume the combination valve (inlet group) is ok as it has been changed and the problem persists.

My thought is that if you run that hot bath to get cold water flowing into the cylinder and also run some cold taps until they run cold you should now feel all three pipes to the combination valve are cold.

Now let the cylinder water heat up without opening any taps or flushing toilets.

Leave as long as you can and keep feeling the pipes to the combination valve.

I would expect conduction to first warm the cylinder inlet pipe as far as the combination valve and then progress to the other two pipes.

This would give you the warm water in the cold pipes that has to be dispersed through the cold taps. It would still be fresh mains water but would be warm initially.

Any other possible conduction from close hot and cold pipes would give the same symptoms and would still be safe as long as the water from the cold taps is not hot enough to scald someone. So just a bit of a nuisance.

Only if hot water from the cylinder is crossing through to the cold through a faulty mixer tap or shower or something would you have a cause for concern due to contamination.

I'm not sure how you would tell if this was the case.
 
Hi, I am not aware I can isolate the HW supply, not sure if you or anyone can tell me how i may be able to do this.

However, what i did just try is to isloate the cold water using the blue valve on what i think is the balanced cold water. I then turned on several cold taps and no cold water (once it had drained off). However, i turned the showers to full cold but they continued to drip. It wasn;t just a slow drip either, more of a drizzle and it has done that for 20 mins so assume it is not just cold left in the pipes, especially as this is only happening with the showers.

THe water then turned warm and stayed warm and the dribble still continues.

Could this be connected and a sign of something or is it a different problem?

I can remember 2 things when talking to the plumber a while ago when he first started to try and resolve this.
1. HE said the shower may have a faulty non return valve on them and hence the problem, however, i then saw in the instructions that they didn't come with them but he then said they were not needed due to the type of system we have and it balances it itself.
2. When it was initially installed, when we wanted hot water, the central heating would come on. THis seemed to confuse him but eventually we had to take up the carpet and floor board upstairs and he said he had to put in another pipe. I have no idea why but he did say there were 2 ways to resolve the problem but putting in an extra pipe on the return, or something, would be the best way to sort it. In fairness, it did, but could that be connected. I can try and find out the exact explanation from my wife if it helps but just thought is is connected.

This is just a nightmare:(
 
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Endaxi, thanks for your input again and i will be trying the bath scenario later.
 
If it was me onsite, I'd be tracking your cold water supply pipework from where it comes into the house all the way up to the combination valve. This will confirm whether the cold is being warmed by the CH or HW pipework and this is just a case of thermal transfer.

Once that's been ruled out then I would go on to look for other potential issues. To confirm though, it isn't right and it shouldn't "just work that way"
 
Hi all, just an interesting update if anyone can add anything.

This morning before any taps used I checked the warmth of the pipes. The system had been running for about 90mins. The cold inlet pipe going in to the cylinder was fairly cool but the 2 pipes above the combination valve were actually feeling that bit warmer.

Firstly I noticed that there was a constant drip in the tundish.

Also, I then only ran the hot tap. I felt warmer water in the cold inlet pipe that was previously cool. I am not sure whether that warm water went down from the supply or up from the cylinder but either way that pipe definitely got momentarily warmer before going cool.

Having run the hot tap for quite a while I then turn a cold tap on. The same 30sec process happened


Does that help explain anything, apart from there is definitely a cylinder issue as I assume the tundish should not be dripping.

Thanks as always
Phil
 
The 2 pipes above the valve are - at the front - the cold mains supply into the valve and behind the balanced cold heading out to what ever it supplies.

The constant drip from the tundish is either the Expansion Pressure Release Valve on the combination valve, the Temp Pressure Relief Valve on the unvented cylinder that's passing or the Pressure Relief Valve for the central heating is passing. Your qualified engineer should be checking and confirming which one it is. Once that is known will dictate whether a valve needs checked/replaced or if the Unvented's internal bubble needs re-instated.

Running the hot tap lets the mains cold flow into and through the valve and into the cylinder then out through the top to feed the HW circuit. If the mains cold pipe feeding the combination valve is cool then getting warm and then cooling down again then it has to be absorbing heat prior to it getting to the valve, that would usually be from a warm/hot pipe sitting next to it allowing thermal transfer.

What cold tap is it you turn on, one that's in the bathroom? Do you know what outlets the balanced cold supplies? I'm still leaning towards the cold mains pipe is sitting next to a central heating pipe somewhere. If it takes 30secs to clear to cold water from warm then sounds like it's running side by side for a fair distance.
 
Plumbing 101...

When running an array of pipes, the hot pipe(s) should always be run above the cold pipes(s) and be insulated where possible.

But, I've seen so many installs where they're all just bundled together like the twined braids of a rope.
 
Thanks guys, unfortunately I can't get to the pipes unless I get all the carpet and floorboards up which is just a nightmare but surely every supply to every tap is not wrong, especially going off in different directions in the house and for 20-30secs of warm then that is why I thought it was something to do with the hot warm somehow passing in to the cold supply.

Could the plumber therefore be right to say it is just down to being a warm house?

Rob, the cold pipe feeding the combo valve just stayed a bit warm to the touch, even for a while after turning the tap on but the cold pipe after the valve going in to the cylinder was the one that felt cool but then felt some warmth when the hot tap was turned on, before going cool again, even though it sounds as though the water goes down it so in theory, either warm water went up it or the cold water going down it was already warm.

To answer your question though, the warm water comes from all taps but once one has been run to get rid of the warm, any tap in the house then only runs cold, until an hour or so later when we get the same problem again.

All cold taps are supplied by the balanced cold from what I know. It's running the kitchen which is biggest problem as takes ages just to get a glass of cold water.
 
As said before. Turn your heating off for a few hrs and see if you continue to get the issue. If you do, turn CH and HW off (so primaries don't get hot) for a few hrs and see again.

If it stays cold after either of those tests, then run a hot tap (one by one) and after each, quickly test cold in kitchen.
 
I'm home all day tomorrow so yes I'm going to try that, thank you.

The underfloor heating is also connected so do I turn that off at the same time as the central heating or just leave on throughout?

Many thanks
 
You are trying to rule out the following causes:

1. Expansion of HW back up the cold pipe when the tank is being heated
2. Thermal transfer from another pipe to the incoming CW feed to the combination valve (this could be any of the heating circuits)

Try turning each one off in isolation and seeing if the problem persists.
 
It's difficult to do as we may obviously use a toilet, tap, dishwasher etc and as soon as the cold water has been used it is the 'normal'.

I did try turning off one at a time, UFH, CH, HW but still got the problem but will try again but wasn't sure if the UFH should be off at the same time as the CH if that uses any of the same pipes.
 
Forgot to say, what I did notice is if only one was on the warmth of the water wasn't as much, but still wasn't sure if that meant there was less pressure from the tank or less heat in the pipes but as you say, it's one of those two issues I'm trying to work out, without pulling up floorboards unless really needed.
 

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