Unvented system - hot water not very hot.

[teecee90]

We have an oldish Tribune Premier TP150B unvented indirect hot water cylinder. It has two tank thermostats - I think the upper one controls the 1.5kw immersion heater and the lower one controls the gas boiler. When relying solely on the boiler, the water never seems to get very hot. This evening the water was barely luke warm so I hit the boost button on the controller to fire the boiler up, but it did not fire. I checked the thermal cut-out buttons on the thermostats and neither appeared to have tripped. The temperature setting on the upper thermostat was set to maximum and the lower thermostat was set very slightly below maximum. I turned the lower thermostat to maximum and the 2 way valve promptly opened and boiler fired up. Looking at the instructions for the tank it says that the 'low' setting on the thermostats is 43 degrees and the high setting is 70 degrees. There is no way that the water was even at 43 degrees but the boiler only fired when I set the thermostat to the maximum setting. Does this indicate a faulty thermostat(s)? The system is probably about 20 years old.

Do thermostats degrade over time or do they just completely fail (all or nothing)?

Would it help to remove and clean them?

Any advice greatly appreciated.

https://i.*********/NIFiS5P.jpg

https://i.*********/zufAfbF.jpg

 

[teecee90]

It was previously 500mm D1 maximum length to tundish, but recent years was changed to 600mm.
The instructions and regulations description and drawings can be a bit confusing I must admit.

This was the original wording: "..The tundish shall be located not more than 500mm horizontally from any valve discharging to it" which taken together with the diagram makes me think it was installed correctly at the time.

The wording has now changed to: "..with no more than 600mm of pipe between the valve outlet and the tundish"

 

[teecee90]

I am intrigued, how have you done that ?

With a pressure gauge on the shraeder valve on top of the vessel in the loft.

 

[townfanjon]

😀

With a pressure gauge on the shraeder valve on top of the vessel in the loft.

So thats how you do it is it !!

 

[teecee90]

😀

So thats how you do it is it !!

It's how I did it. Why, what have I done wrong?

 

[townfanjon]

It's how I did it. Why, what have I done wrong?

Cant say , its a secret

 

[teecee90]

Cant say , its a secret

That's helpful. Thanks for your contribution.

 

[ShaunCorbs]

Yea you done it wrong and will give a false reading

 

[townfanjon]

My contribution is very simple my friend , working on an unvented cylinder requires a qualification that we have to pay for , it maybe your cylinder but you are not qualified to work on it , do you touch your boiler when you are not qualified to work on it ? , I hope not

Thats why its a secret

 

[teecee90]

My contribution is very simple my friend , working on an unvented cylinder requires a qualification that we have to pay for , it maybe your cylinder but you are not qualified to work on it , do you touch your boiler when you are not qualified to work on it ? , I hope not

Thats why its a secret

Nice attitude....

 

[teecee90]

Yea you done it wrong and will give a false reading

All I said was that I had checked it was pressurised, not that the reading was correct. I checked it was pressurised the day before the engineer came to service it. He did go into the loft so I assume he checked the reading, although presumably he wouldn't have been able to get an entirely accurate reading himself with it still in situ?

Anyway, its obvious this thread isn't going anywhere so this will be my last post.

 

[Best]

Other people could read this thread and use any advice to work illegally and dangerously on their, or others unvented cylinders, so that is why information given is limited