My Thermalstore - is it Vented / Unvented?

[Brix]

Hello folks.

My thermalstore heating (hot water and UFH) system was installed almost 20yrs ago. It has consistently caused confusion for engineers who often seem to confuse it with a megaflow type install.

The main body of water in the tank in in a closed loop to the Potterton boiler. The boiler heats this body up. Cold water (at mains pressure) and UFH heating water are passed through stainless steel coil exchangers in the tank and take energy from the body of water as they pass through but never contribute to the water volume or pressure in the tank.

The system has been described to me as vented, unvented and hybrid. I have been told that it requires certification to work on. And that it doesn't. That by law it requires annual maintenance and sign off, and that it doesn't. That this type of installation is at risk of explosion. And that it's not.

The company who supplied it went bust shortly afterwards so no help there and there is no makers mark on the tank (came from N Ireland, I think).

Any expert advice gratefully received. I'm in UK.

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(The pre assembled module referred to in the diagram is the UFH manifolds, pumps, flow and returns etc..)

 

[SJB060685]

Looking at that I'd say its unvented, which does require a qualified person to work on.
Definitely no tanks in the loft?

 

[Brix]

Looking at that I'd say its unvented, which does require a qualified person to work on.
Definitely no tanks in the loft?

Thanks. Definitely no tank other than thermal store itself. Just automatic air vent and expansion vessel.

 

[Roy_66]

Hi Brix,

Interesting system.

Now I've no plumbing qualifications, so just a personal view:

If/when the heat exchanger tank fails internally the whole thing will pressurise up. The pressure reduction valves have limited lifetime so should be checked periodically by an expert in any case.

Silly question: how do you top up the boiler side? Is there a filling loop for that? I note the AAV, but no sign of a header tank (see prev posters question).

So if it were mine I'd consider it unvented and get an expert in.

Other silly question if you had it converted to vented, is there space above for header tanks. Also consider structural support for such tanks and risk of leaks. Get expert advice again.

Cheers,

Roy (rank amateur)

 

[Brix]

Hi Brix,

Interesting system.

Now I've no plumbing qualifications, so just a personal view:

If/when the heat exchanger tank fails internally the whole thing will pressurise up. The pressure reduction valves have limited lifetime so should be checked periodically by an expert in any case.

Silly question: how do you top up the boiler side? Is there a filling loop for that? I note the AAV, but no sign of a header tank (see prev posters question).

So if it were mine I'd consider it unvented and get an expert in.

Other silly question if you had it converted to vented, is there space above for header tanks. Also consider structural support for such tanks and risk of leaks. Get expert advice again.

Cheers,

Roy (rank amateur)

Cheers. Yes - a filling loop by the boiler.

I had all the safety valves replaced about 18 months ago when it was last drained down. Nevertheless, I believe that it did actually over heat recently causing a pipe between the tank and boiler to burst, emptying the tank. The engineer bypassed the burst pipe and left it in situ so could not see the damage. It seems like both the stat and the safety cutout failed on the immersion and then the pressure relief valve failed. 😬

Sorry if my responses are not in order - they are being held for moderation.

 

[SJB060685]

If/when the heat exchanger tank fails internally the whole thing will pressurise up

As I said above this is an unvented thermal store based on the image. Meaning if it were to fail you will lose a very large volume of water.
The only reason reason I asked if the there was header tanks in the loft was because the OP is unsure.
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If the heating source temperature control failed you are incredibly lucky there was no explosion if the combined temperature and pressure relief valve failed as well. Anyway this is an unvented appliance and needs a qualified engineer to service and maintain

 

[Brix]

As I said above this is an unvented thermal store based on the image. Meaning if it were to fail you will lose a very large volume of water.
The only reason reason I asked if the there was header tanks in the loft was because the OP is unsure.
[automerge]1597852363[/automerge]
If the heating source temperature control failed you are incredibly lucky there was no explosion if the combined temperature and pressure relief valve failed as well. Anyway this is an unvented appliance and needs a qualified engineer to service and maintain

Thanks. It was quite dramatic and I did think it might blow. Can you think of any reason this could have been instigated or exacerbated by water being shut off in the street and then back on (Thames Water maintenance)? When I went to bed there was no water - by 2am the tank was whistling before the pipe burst (pipe in closed tank>boiler loop).

 

[SJB060685]

I think its just an untimely incident.
Which part if the system ruptured? If it was on the heating side then that should not of been affected by the water works.

 

[Brix]

I think its just an untimely incident.
Which part if the system ruptured? If it was on the heating side then that should not of been affected by the water works.

It was the flow from the boiler to the tank. So protected from mains. I can't see how it could have affected it but such a weird coincidence!

 

[Warmiger]

I can’t see it causing it to fail.
These always use to confuse our engineers as some of them have a header which is for the f&e. Sometimes combination cylinders would get ordered instead by mistake.
As you stated you have a filling loop so you won’t have a header tank.
They normally give good hot water pressures with unlimited hot water and work well until the heat exchanger starts to scale up.
I would get rid of the thermal store as very inefficient. I would get an unvented cylinder installed as a replacement as will save you quite a lot of money in energy in the long run.
Thermal stores are expensive tanks so should work out cheaper in the long run. I use to work on a policy where we had to replace like for like so that was the only time we installed them. No one ever asked for them.

 

[Brix]

I can’t see it causing it to fail.
These always use to confuse our engineers as some of them have a header which is for the f&e. Sometimes combination cylinders would get ordered instead by mistake.
As you stated you have a filling loop so you won’t have a header tank.
They normally give good hot water pressures with unlimited hot water and work well until the heat exchanger starts to scale up.
I would get rid of the thermal store as very inefficient. I would get an unvented cylinder installed as a replacement as will save you quite a lot of money in energy in the long run.
Thermal stores are expensive tanks so should work out cheaper in the long run. I use to work on a policy where we had to replace like for like so that was the only time we installed them. No one ever asked for them.

I forget exactly why I chose a Thermal store, but a combination of unlimited hot water, potable and mains pressure.

Why are they inefficient - is it because they hold water at a higher temperature?