Vent and Feed - which order?

[DavidMG]

Hi,
I have a standard gravity fed indirect hot water system and pumped central heating system supplying 12 rad's. The vent and feed from the F&E tank are connected to the gravity fed pipes close to the hot water tank. The hot water coming from the boiler connects to the bottom of the hot water tank heat exchanger and tees off to the F&E feed. The top of the heat exchanger tees to the F&E vent and the return to the boiler. I had a problem 5 years ago with a blockage where the F&E feed joins the system, just where it sizes down to 15mm. At that time I replaced some piping, desludged and inhibited. Now I have intermittent hot water and suspect the same is happening again. I checked the F&E tank and there is a lot of brown sludge and some black particles too. I banged the F&E feed at the point where it blocked last time and my hot water is working for now. I intend to flush out, clean with 2 litres of X800 (more aggressive than what I used last time) and inhibit with 2 litres of X100. My questions are:
Does the sludging indicate that the old inhibitor has failed due to dilution over the years (no obvious leaks) or will it occur even in a properly protected system?
Are the feed and return to the hot water heat exchanger around the wrong way, as I suspect, and if so will that cause accelerated corrosion by drawing air into the system?
Would the hot water heating become more efficient if I reverse the pipes?
I have a lot of boiler kettling too - is the X800 likely to help with this?
Any advice would be welcome.

 

[namsag]

The usual way on a gravity system would be flow into the top connection of cylinder with the open vent off the top of a tee. And return off bottom connection with cold feed into top of tee

 

[bengasman]

I would not call a gravity system "standard", but antiquated.
Chances are you have about half a century's worth of limescale and corrosion build up which needs removing properly.
After that is done, you will probably find the problems are solved, as any installation fault would have presented itself several decades ago.

 

[DavidMG]

Thanks for the responses - need a bit more help with this though please.

Five years ago I used Fernox Restorer (the gentle one for older systems) and then Protector (MB-1) and Boiler Noise Silencer. At the same time I replaced the blocked 15mm feed pipe, the pump, the pump gate valves, the zone control valve and a number of faulty TRVs that some fool had installed the wrong way round (these were directional, although I realise that some these days are not). I have little confidence in the installation and would not be at all suprised if someone had connected the hot water pipes around the wrong way too, presumably at the boiler end (the boiler has I think been resited and has certainly been replaced since the original system was installed). Further evidence of a botched installation is provided by the fact that the largest double radiator is in the smallest bedroom, and has been installed so as to block access to a double plug on the skirting board. Anyway, the old components that I replaced five years ago seemed reasonably clear of sludge and scale, other than the pump impellor and chamber. The zone control valve had become stiff but was otherwise clean. After using the Restorer I was reasonably confident that the system was cleanish and did check the F&E tank again for sludge and other debris after a few months - all seemed ok but the boiler was still kettling.

I am now concerned, five years on, because F&E tank has brown sludge and black particles back again and I think that the F&E feed has blocked again.

To reiterate my questions:

Is X800 likely to help reduce the boiler kettling?

Is this sort of sludging, over 5 years, normal for an old system (that was certainly not whistle clean) or does it indicate that the inhibitor is not doing its job (presumably due to dilution)?

Is it worth my swapping the flow and return pipes to the hot water coil over (I don't want to do it unless someone can tell me that it would certainly be causing problems)? The arrangement seems correct, with the vent off the top of the high tee and the feed off the top of the low tee, but unfortunately the boiler water flows to the low tee rather than high tee - does this matter? Could it be causing the problems?

Many thanks.

 

[Agile]

Your system is incorrect because the vent pipe MUST be directly connected to the flow pipe out of the boiler. Potential safety issue there.

If it is a gravity system then its a little surprising that it works very well because the coil connections that way will act against gravity flow.

Connecting for gravity should be the other way round with flow to the top.

Flow to the lower connection is still good for a PUMPED system as it will heat it quicker although not quite so efficient for a condensing boiler.

You probably need several different chemicals to properly treat your system.

Tony

 

[DavidMG]

Ok - now I am worried.

I have checked the boiler connections (Potterton Netaheat Electronic 16-22) and they are as follows:

Gravity HW from boiler 28mm immediately to zone control valve, thence several yards primarily horizontally to lower hot water tank coil connection and tee to 15mm cold feed. Upper hot water tank coil connection tee to 22mm vent and 28mm return to boiler.

Pumped CH from boiler 22mm immediately to pump, thence rad's and 22mm return to boiler.

I accept that the HW flow through the coil is wrong and maybe it isn't that efficient - our gas usage is certainly pretty high. But perhaps the volume of water cooling in the coil is not that significant when compared to the volume in the supply pipes and possibly the water velocity is not reduced by much.

But, given the system is the way it is and has been for at least 16 years, my concern now is that when the hot water timer is off the system has no vent !??? Could that be why someone has reversed the coil connectors - i.e. to give shorter access to the vent via the HW return when the hot water zone valve is closed?

The boiler also does kettle a lot and the pipes bang away, particularly when warming up from cold in the winter. I presumed this was due to scale rather than plumbing faults.

Help ....

PS Even if I just leave the plumbing as it is and merely desludge again what chemicals should I use to clean it given its age?

Thanks.