Unvented Hot Water Cylinders.

Exodi

Belenus said:

I will post a few pictures that show that better than I can describe.

That would be good, I'd be quite interested in doing the same at my house.

I really have no idea what my tank temperature is.

I usually set the programmer to call for heat to the hot water for 15 mins in the morning and 30 mins in the afternoon. Water doesn't go cold for 2 people with average use. I play around with it occassionally trying to shave off an extra 5 minutes now and then.

I'm not sure how a thermometer would work as I always expected the hottest water would sit at the top of the tank and the coldest at the bottom - but it's a useful guide no doubt.

Belenus

Here are pictures of a close up of the probe, the boiler cupboard and the boiler with the covers removed. 

The white wire to the right is the incoming mains power. The black wire is the probe which you can see emerging from the insulation in the close up photo and on the top of the cabinet. 

Belenus

Exodi said:

Belenus said:

I will post a few pictures that show that better than I can describe.

That would be good, I'd be quite interested in doing the same at my house.

I really have no idea what my tank temperature is.

I usually set the programmer to call for heat to the hot water for 15 mins in the morning and 30 mins in the afternoon. Water doesn't go cold for 2 people with average use. I play around with it occassionally trying to shave off an extra 5 minutes now and then.

I'm not sure how a thermometer would work as I always expected the hottest water would sit at the top of the tank and the coldest at the bottom - but it's a useful guide no doubt.

A temperature probe, or thermometer as you call it, works just fine. It is as you say a useful guide. Even if it is not particularly accurate you will soon learn to judge the amount of hot water available.

Yes, the hottest water is at the top of the tank but there is not a huge temperature gradient in the top two thirds of the tank. Even if there is a large temperature gradient, you will again soon learn what are the ideal temperature settings.

The hot water sensor for our Powermax is well below half way down the tank. If you look at the picture above you can see a rectangular black and silver label with the top right corner slightly peeling off. Below that you can see a white wire emerging and trailing upwards to the control panel. That is the hot water temperature sensor.

Exodi

That's all very useful, thank you very much!

ComicGeek

While I'm a big fan of energy efficiency and saving money, I can't quite see the point of a temperature probe in a fairly small hot water cylinder.

You work out what the minimum storage temperature you can get away with, and set the cylinder stat to that. Domestic cylinders are too small to have significant stratification. You then set your heating programmer to heat the cylinder for a particularly period each day, rather than being demand led (ie kicking the boiler on every time you run the shower). The boiler stops heating once the cylinder is at temperature. 

Why make it more complicated than it needs to be? Keep the cylinder at temperature and then you know you've got enough hot water, no need to check another sensor. 

plumb1_2

• gas valve settings on this boiler are known to drift over time. These need checking and recalibrating (if required) on every annual service. If the settings are not correct, carbon monoxide can be produced in vast quantities.
• Flue gas readings can only be taken from the flue on this boiler where it exits the building. One engineer cannot monitor the flue gas readings outside at the same time as adjusting the gas valve inside. Poor or non-existent servicing of these boilers has turned them into carbon monoxide-producing death traps.
• The burner gasket is of a poor design and prone to leakage. A new gasket MUST be fitted every time the burner is removed for servicing according to Potterton-Baxi technical support. These gaskets are hard to source. I suspect few actually get replaced on servicing. Leaking fumes from the burner gasket has apparently led to the deaths of a number of users of Range Powermax boilers.
• This boiler produces condensate in the flue. It was never designed to condense and has no means of discharging the condensate produced in the flue. The acidic condensate eats in to the aluminium flue wall. After several years of operation the flue becomes porous and allows flue gases to discharge in to your property.
• The aluminium twin-tube flue system used on this boiler is very compact and was designed to be installed in ceiling voids, behind walls and in boxings. Instances of the failure of flue joints are not uncommon and often allow flue gases to discharge directly into living spaces. When a flue is concealed within the fabric of the building it is often impossible to inspect the flue or the joints for integrity. Several people are known to have lost their lives due to leaking concealed flues. There are now compulsory Gas Safe procedures for concealed flues due to the dangers they can hide.

These boilers can be silent killers; they have killed before and will kill again. For this reason we will not service or repair these boilers. In our opinion these boilers should be replaced at the earliest opportunity, before they kill yet another person.

Belenus

Thank you for that but you are referring to the Potterton Powermax discussed here. These date back to the 1990s.

Our boiler is the Potterton Powermax HE, a different boiler that replaced the Powermax and, as far as I am aware, does not have all the problems that you detail. Ours dates to 2004/5.

Potterton should probably have dropped the Powermax name and called the Powermax HE something else.

None of the Gas Safe people, including Potterton/Baxi staff, who have repaired or serviced our Potterton Powermax HE boiler in the last 11 years, have ever suggested that the boiler is unsafe.

We have a CO detector in the boiler cupboard.

Snuggles

Belenus said:

ComicGeek said:

 Megaflo is just an expensive type of unvented cylinder - good quality, but priced more for the high end market. Lots of cheaper options available that are fine for most people. 

Megaflo is just an expensive type of unvented cylinder - good quality, but priced more for the high end market. Lots of cheaper options available that are fine for most people.

We will investigate other options.

One thing that puts us off the Megaflo is the need to service or reset the internal air gap device annually. Other alternatives have an external expansion tank.

We have plenty of room in the boiler cupboard so we have no space issue with an external expansion tank, There is one there already for the Powermax although we would replace that with new as it is 17 years old and counting.

Do you have your Megaflo serviced annually or is the air gap thing a DIY job?

Any unvented system is supposed to be serviced annually I believe (not just the Megaflo).

We have an unvented cylinder with an external expansion vessel and the person who services our boiler every year also checks the unvented cylinder, vessel, pressure relief valves etc. The vessel often needs re-pressurising (and occasionally replacing - I think we've had to replace ours about three times over the last 16 years).

They are supposed to be checked regularly because I believe there is risk of the cylinder exploding if all of the safety mechanisms fail - vanishingly rare, but not something I'd want to leave to chance.

 

Taff76

Looking to replace my unvented water cylinder, does anyone have knowledge/experience of the Dimplex Quantum water cylinders?  Thinking this will match up with my Quantum storage heaters.


Thanks