3rd system in 12 years

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JohnH74

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OK, I last posted in here in 2009 with guidance given on a new system.
https://www.diynot.com/diy/threads/thermal-store-heat-bank-or-two-combis.170502/

At the time I was running 2 combi's twinned to supply whole house.
In the 2009 post I was looking for guidance into a replacement system as the combi's had broke.

We opted for an "Advanced Appliance" 300L thermal store with in-built heat exchange fed by a Vaillant boiler. We never got round to the alternate heat sources.
Well anyway, we think the thermal store is knackered as the expansion tank is going past 3bar and causing the overflow to pour out (imagine a nice hot spring pouring down the drain). We have disconnected the water feed into the expansion tank and this issue is still there.
We, therefore, thought that it is backfilling from the store as there is no other way for it overflow.

So anyway, if this is the case; I am left with a reasonably new Vaillant A rated condensing boiler with my options:
1) another thermal - expensive considering we do no have the alternate fuel source
2) unvented tank
3) some kind of maxiflow combi which will be big enough to cover all needs.

6 bedrooms, 5 teenage children and 4 bathrooms = constant demand.

Firstly, thoughts on current fault
Secondly, thoughts on replacements so that I do not need to spend another £2k every 5 years.

ps - I get professionals to do the work but they all have their own preferences on what is best.
 
I have a 300 stainless steel thermal store with 100kW external plate heat exchanger that is no longer needed if you want to make me an offer.

A few cosmetic issues due to screwing assorted data loggers and gubbins to the outer shell.

Store is rated for pressurised use on the boiler side. Might need a new safety valve - I'd have to check if it is still stuck to the side.

100 litre expansion vessel also available.

Store has a separate coil fro alternative fuel sources and big tappings if you have solid fuel - can't be used as a sealed unit though with this.

Cost about £2k when new.
 
Thanks Dan, I wasn't contemplating a refurbed model. How old is it and how much use has it had?
Not bothered about cosmetic issues but need it to work. Ours is currently a sealed unit as no space for header tank (if that is required)
I am thinking the biggest cost of fitting another thermal store will be the labour though.
 
Ha Ha Roger,
I do remember BB getting some abuse.
To be fair it was probably a classic case of a little bit of knowledge in uneducated hands. My installer also thought it was a good idea.
What would you opt for?
Just had a quote of £4400 for installation of Worcester 550 CDI Highflow combi or £2300 for installation of a 300L unvented cylinder.
Seems very expensive.
 
Are you sure you don't just need a new expansion vessel, or even just need the existing one recharging?
 
Its a good question Muggles....
I have had 2 heat engineers out who couldn't understand why it was leaking (one couldn't even understand how the system worked)
We have disconnected the expansion vessel from the main feed and it still happens.
It only stops when stopcock is off.
Last plumber has also recharged the expansion vessel and the one in the boiler (made no difference).
Guys at Advanced (telephone support) have no idea and therefore assume it is a knackered store.
 
Is it going over 3 bar all the time, or just when it's heating up/hot?
 
It is over 3 bar all the time.
I switched off the boiler (to remove the only heat source) this morning.
Came home to find that water was still pouring out like an open tap (just cold this time)
Only time water pressure drops is when we completely switch off the water
Does this make a difference as to whether it is the expansion or the store?
 
JohnH74 said:
Ha Ha Roger,
I do remember BB getting some abuse.
To be fair it was probably a classic case of a little bit of knowledge in uneducated hands. My installer also thought it was a good idea.
What would you opt for?
Just had a quote of £4400 for installation of Worcester 550 CDI Highflow combi or £2300 for installation of a 300L unvented cylinder.
Seems very expensive.
Click to expand...

I had it made back in 2009 (roughly). It was used (on softened water) for 3 years while I was experimenting with a boiler control method.

Took it out and put it in storage.

It's one of these :

https://drive.google.com/file/d/0B6V-Gyu0ykkgZlJBdlNzSy1rNjQ/view?usp=drivesdk
 
JohnH74 said:
Came home to find that water was still pouring out like an open tap (just cold this time)
Only time water pressure drops is when we completely switch off the water
Does this make a difference as to whether it is the expansion or the store?
Click to expand...

Is it a sealed thermal store integrated with the heating system?
Normally the filling loop is disconnected when the system is filled. Usually to about 1 bar.
An expansion vessel is sized accordingly to cater for the extra expansion.
If the filling loops is connected and you're leaving this turned on then its no wonder you are having problems.

You say two heating engineers have looked at the system?

Is this your thermal store?
https://www.advanceappliances.co.uk/content/images/products/74/main/ENERGY MANAGER INST GUIDE 24.07.17.pdf

It is possible that the internal phe has failed and the system is being pressurised by the mains.
I'd never buy a contraption that had a phe fitted inside the store.
 
Last edited:
Roger928 said:
Is it a sealed thermal store integrated with the heating system?
Normally the filling loop is disconnected when the system is filled. Usually to about 1 bar.
An expansion vessel is sized accordingly to cater for the extra expansion.
If the filling loops is connected and you're leaving this turned on then its no wonder you are having problems.

You say two heating engineers have looked at the system?

Is this your thermal store?
https://www.advanceappliances.co.uk/content/images/products/74/main/ENERGY MANAGER INST GUIDE 24.07.17.pdf

It is possible that the internal phe has failed and the system is being pressurised by the mains.
I'd never buy a contraption that had a phe fitted inside the store.
Click to expand...

Yes, that looks like it.
It is a sealed system with the only feed in being the cold water which goes's in to be heated.
When we turn this feed off, there is no water available through the hot taps but the pressure does drop in the expansion vessel.
(when I say no water, it trickles out basically emptying the upstairs radiators)

The system boiler and the expansion tank link back into the store in a couple of places.
I think the idea is that the boiler acts like a combi boiler if there is insufficient heat in the store.

It did, kind of, work for 7 years so I cannot believe the plumbing is wrong, but you do have me concerned about the plumbing set-up now.
Our issue over the past 7 years was it didn't give enough heat, and not that it was overpressurised (in fact, for about 3 years it was constantly losing pressure). We maintained it at 1 bar for years.

There is a cold feed into the expansion vessel but this is usually "off" on both the taps. Whilst this fault has been occurring has been permanently disconnected.

1 engineer visited twice and couldn't understand it.
2nd engineer visited, claimed to understand the system but couldn't find a physical fault with it.
The conclusion therefore was it was the store.

Your final comment of the internal phe failed and being pressurised by the mains seems the only sensible option.
Obviously, this cannot be repaired and Absolute do not build them internally anymore.

I've resigned myself to it being knackered but have not picked a replacement system yet.
Also, I am having a nightmare getting an engineer to come out and actually swap it over.
10+ emailed with only 1 reply with a very very high quote.
Guess nobody wants the job.....
 
picasso said:
How do you top up the pressure in your central heating system ?
Click to expand...

The only way I have ever had a need to top up the pressure was via the flexible hose tap that fed into the expansion vessel.
I used to have to do this all the time as it was losing 1bar every month ( I assumed there was a small leak somewhere).
For a few years, I didn't have to do anything and it was static around 1 - 1.5bar.
In the last 6 months it has been overpressuring and right now it fills above 3bar within 30seconds of draining it.
 
Surely advance appliances will honour their warranty and supply you with a replacement unit?

Quite possible to fit an external phe also.
But that modification would almost certainly void any warranty or guarantee.
 
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