Flowmax 140 thermal store Feed & Expansion tank full of steaming hot water.

[Vacheron]

Hi All

Just wondering if anyone familiar with thermal stores could offer some assistance.

We inherited the system below when we moved into our house in 2010.

The system consists of a Potterton Suprima 60L boiler located in the Garage and Flowmax 140 Thermal Store in the loft.

Recently I have noticed that there is a trickling / pouring noise coming from the loft whenever the pump is running. On investigation the expansion tank was steaming with hot water. Shining a torch in the feed and expansion tank showed that the underwater expansion pipe which comes from the bottom of the hot store was pumping hot water into the expansion tank.

There is no sign that the overall height of the water was increasing significantly, nor has any water reached the overflow which I guess also rules out a leak in the heat exchanger, it seems more like the submerged expansion pipe is "breathing" hot water in and out of the expansion tank.



My thoughts are that perhaps air has accumulated at the top of the hot store? This would explain the pouring noise as the pump pushes hot water from the boiler out of the upper tank inlet above water level, and the higher expansion of the air at the top of the tank could be resulting in the increased "breathing" of the expansion pipe. However should there not be an air vent at the top of the hot store to prevent this? Do these ever get blocked?

Also, our system (with the pump pulling water from the bottom of the store) also seems a little unconventional compared to the layouts I've seen on the internet. Is this an accepted method, or something that could also cause the problems I have?

Thanks in advance:
Paul.

 

[Vacheron]

Just an update for those searching for a similar problem. I had a chance to get back into the loft today and found the air vent exit from the top of the hot store into the expansion tank. The exit had condensation water sitting in it right to the top of the vent pipe!

A quick poke with a flexible rod resulted in a hiss and an escape of steam and the expansion tank water began emptying into the hot store. This opened the float valve and the resulting cold water feed stirred up about 3cm of sludge in the bottom of the expansion tank so I plugged the expansion pipe with a cork while I cleaned it out.

Once this was done and the water had settled I uncorked the expansion pipe and the entire feed tank emptied into the hot store. Once this was gone, the float valve kept feeding the hot store expansion pipe for another 4-5 minutes before it topped off and the expansion tank began to fill again.

The pouring noise when the pump is running is now no more, and with a few quick calculations I estimate that there was approximately 25-30cm of air trapped at the top of the hot store!

 

[Agile]

If there was so much sludge in the expansion tank then imagine how much there will be in the tank itself.

No wonder we call them sludge buckets.

The problem is that no one ever puts the large amount of inhibitor which would be needed to protect it properly.

Tony

 

[Vacheron]

Hi Tony.

I completely agree on all counts.

As mentioned I bought the house (Built in 1989) in 2010. Over time and as necessary I reverse engineered the central heating system and taught myself the basics.

I noticed the poor performance when the boiler kept going into thermal lockout in the cold. This was due to flow resistance plus and you could feel the rads were full of sludge. A sticky 3 pos valve sometimes sticking in position resulting in the CH call signal being jammed permanently on regardless of Thermostat position didn't help either!

F3 did very little as it was packed solid in the rads. I ended up taking all the downstairs rads off, taking them into the garden and connecting a hose to one end and inverting,shaking and beating them with a rubber mallet until the water ran clear. (See attached Pic) sometimes it took 5 bucketfuls water as shown before one radiator ran clear! I appreciated that there could still be some sludge still in the pipes after this, but this made a huge difference to the heat transfer and the boiler has been trouble free since.



When I was done I refilled with 3x500ml bottles of Fernox F1 due to the 140L capacity of the store, plus the 11 rads in the system. I'd actually just ordered another 2 bottles for topping it up about 10 minutes before you posted.

God knows I'd love to be able to do the same with the "sludge bucket" in the loft, but that is well beyond my comfort zone or technical ability!

I am hoping that, as the expansion feeder comes from the bottom of the hot store, that the majority of the sludge in the expansion tank could have been brought up from the bottom of the hot store during the pumping action, and so that may have helped clean things out further (a little at least!)