The mystery continues

[lockett]

Hello
At the end of march I posted a question "Cold Water Mystery", this referred to my Atag boiler failing to supply DHW. Just to sum up my post, the boiler would occasionally supply only cold water from the hot taps. The installer changed the flow sensor, no change. It was suggested that the problem was the shower mixer valve, fitted a new shower, no change. After further investigation and tests, it was found that water from the hot tap would run water for 30 seconds (5 sec/Lt) after the cold water to the boiler was shut off. After ruling out the two mixer taps the installer is convinced I have a TMV passing and confusing the boiler.
This is where I really need your advice, despite looking under the sinks, ripping open boxed-in piping and my bath panel, I can't find a TMV any where.
I can't go on ripping my house apart, especially since all my floors are covered in laminate flooring giving no access to under the floor.
Can anyone suggest how I can locate the TMV, if it does actually exist?
If my installer is convinced it is TMV and that is the problem but I can't find it how can we move onto the next stage of the of the fault finding?

Any advice will be much appreciated

 

[vulcancontinental]

Thermal imaging camera?
How often is occasionally?

 

[lockett]

Very good idea, do you have experience of using a thermal imaging camera, would it work through flooring and chipboards?
As it is a random occurrence it's hard to say maybe once a fortnight.

 

[oldbutnotdead]

You might want to run a temperature experiment to try and determine the presence or absence of such a device.
Set the dhw temp at the boiler to something quite high. Get yourself a thermometer that can measure water temp (digital probe type should be faster). Check dhw temperature at the tap nearest the boiler- does it match what you've set the water temp? Try at the shower and bath, see if it gets up to temperature or near enough.
Can you isolate cold to everything except the cold supply to the boiler? If yes then repeat above experiment, see if there are any significant changes. If/when the fault recurs, try it & see if the fault clears
TMV would usually be near the bath in a house. Laminate flooring isn't difficult to lift, the chipboard sheets underneath will be more of a pain

 

[lockett]

Hello oldbutnot...
Can you please resend your post, I didn't get all of your message.

 

[oldbutnotdead]

Hello oldbutnot...
Can you please resend your post, I didn't get all of your message.

Have a look now, fat thumbs hitcsend before I'd finished

 

[lockett]

I see where you are coming from, but if I have a none working TMV which according to the engineer is the problem I have, and it's not regulating the DHW temperature what does this confirm. Or am I wrong in my assumption. I will give it a try, but I can't turn of the water to the bath or the shower, both inaccessible.

 

[lockett]

Just tried the test, DHW set to max temp 65°, ran the tap next to the boiler thermometer reading of 64°, ran the bathroom tap which it a considerable distance from the boiler, thermometer reading 62°. I'm using a normal glass thermometer, so I think with in the scope for errors.

 

[oldbutnotdead]

I see where you are coming from, but if I have a none working TMV which according to the engineer is the problem I have, and it's not regulating the DHW temperature what does this confirm. Or am I wrong in my assumption. I will give it a try, but I can't turn of the water to the bath or the shower, both inaccessible.

The fault is intermittent therefore if there is a TMV fitted it may be working properly most of the time.
Yes it'll be worth setting dhw to very hot - if the temperature at the shower/bath is significantly lower (like 10-15 degrees) then there's some sort of tempering going on.

EDIT Just seen your post- that's not a result I'd expect from a TMV. I would expect a non- working one to fail safe (IE run cold).
When was the place built or bathroom last refurbed?
Just reread your first post- this is a combi isn't it? My combi will emit no hot water (in fact no water from hot taps) if the cold water supply is turned off. Or is there a cylinder somewhere (30 seconds would be right for a decent-sized expansion vessel discharging).

 

[lockett]

Unfortunately reference my last post, I'm not getting that kind of temperature differential.

Still not sure where I can go from here, how can I find the TMV or prove I don't have one without ripping my house apart?

 

[terryplumb]

I suspect you are barking up the wrong tree,and your problem is the boiler . Intermittently not firing up for domestic hot water ,once a fortnight, isn't something I would associate with a thermostatic mixer valve issue,they are not that temperamental.
The next time it happens ,head straight to the boiler and see what it is doing .

 

[lockett]

When it first happened the tap symbol, square around the tap was not there.
The thing leading the engineer to the TMV is the hot water tap runs for 30 seconds (at 5 sec/ Litre) after the boiler is isolated from the cold supply.

 

[oldbutnotdead]

What happens at the end of the 30 seconds? Does it keep running? And is it running hot or not (shouldn't be).

 

[terryplumb]

When it first happened the tap symbol, square around the tap was not there.
The thing leading the engineer to the TMV is the hot water tap runs for 30 seconds (at 5 sec/ Litre) after the boiler is isolated from the cold supply.

Are you telling us that a hot water tap runs for 30 seconds ,giving 12 litres of cold water, and then gives nothing at all after 30 seconds ??

 

[lockett]

Yes, with the boiler cold water supply isolated, hot tap water runs for 30 seconds, then just stops, with no more water flowing.