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.

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[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?

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[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.

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[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