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

 

[ShaunCorbs]

Best to get a G3 engy to have a look at the system and maybe service the cylinder

You need to be G3 registered to be able to work on unvented cylinders

Put the thermostat settings back as they were

 

[teecee90]

The system was serviced last week. The only thing I've changed is to move the lower therm setting about a millimetre to the right.

 

[ShaunCorbs]

The system was serviced last week.

The cylinder or the boiler ?

If boiler cylinder needs to be done and checked by an unvented technician

 

[teecee90]

Both were serviced.

 

[ShaunCorbs]

Both were serviced.

Call them back as it's one of the points to check store water is reaching the correct temperature to prevent legionella

 

[teecee90]

I have no faith in them. This isn't the first time Ive had problems with them. Would be helpful to have a clue what the problem might be so I can get someone else in if necessary. Could an electrician deal with the thermostats?

https://i.*********/J7Wc1hX.jpg

 

[ShaunCorbs]

Any chance of a pic of the whole cupboard? Eg whole cylinder and pipes

And no anyone working on an unvented cylinder needs to be G3 registered

 

[teecee90]

Any chance of a pic of the whole cupboard? Eg whole cylinder and pipes

And no anyone working on an unvented cylinder needs to be G3 registered

Yes of course..... there are two 2-way valves at the back of the tank - both were replaced 2 years ago. There is an expansion vessel in the loft.

https://i.*********/DKHSXCM.jpg

 

[ShaunCorbs]

Who ever serviced that wasn't G3 registered

D1 should be no more than 600 mm and yours is listed at 1200mm

So it makes you think what ever else they missed

 

[teecee90]

Okay, well I think I'll get the thermostats replaced. It's a pretty simple system really and I can't see what else could be the problem.

 

[townfanjon]

Okay, well I think I'll get the thermostats replaced. It's a pretty simple system really and I can't see what else could be the problem.

Good look on locating the stats , sorry you may struggle , but good luck .
I havnt read everything above but has there been water running through the tundish ? , did the engineer go into the loft ?

 

[teecee90]

Seems to be plenty of those thermostats available online - S6211

There is no leakage from the TP valve and the expansion vessel is properly pressurised

 

[Best]

Seems to be plenty of those thermostats available online - S6211

There is no leakage from the TP valve and the expansion vessel is properly pressurised

How do you know the expansion vessel is properly pressurised?
The engineers you said yourself you had no faith in them, plus you have faults unrectified

 

[Best]

Strange the engineer wrote 1200mm D1 length, but then didn't correct it or note it on the Observations part of form.

 

[teecee90]

How do you know the expansion vessel is properly pressurised?
The engineers you said yourself you had no faith in them, plus you have faults unrectified

Because I've checked it myself.

Must admit I don't understand the D1 issue - can anyone explain? As far as I know nothing has been changed since the property was built, other than replacement of the motorised valves, anode & TP valve a couple of years ago.

 

[ShaunCorbs]

Because I've checked it myself.

Must admit I don't understand the D1 issue - can anyone explain? As far as I know nothing has been changed since the property was built, other than replacement of the motorised valves, anode & TP valve a couple of years ago.

From the safety valve the black tundish needs to be within 600mm

So it wasn't right from day one

 

[teecee90]

I might be wrong, but looking back over previous versions of the regulations, at the time the house was built it seems that the requirements was for the tundish to be a maximum of 500mm from the valve measured horizontally and for a minimum 300mm fall after the tundish. There is no mention of a maximum pipe length between the valve and the tundish, although later regs set this at 600mm. So, it wouldn't meet current regs but was probably okay at the time it was built.

https://i.*********/k8vo0Ri.png

 

[Best]

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.

 

[townfanjon]

Because I've checked it myself.

.

I am intrigued, how have you done that ?

 

[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