Air lock(s) or sludge blockages?

[feynman]

Weird one this. Some radiators sometimes get warm sometimes they remain cold. (but not because of the TRV's or room stat, or boiler stat or boiler overheat stat - all those are normal and set appropriately).

We have tried every combination of CH and HW. Both zone valves move and work correctly when their respective thermostats demand heat.

The pump runs and has been bled of air, and I can hear that it is full of water internally.

The boiler feed pipe to the pump gets hot as normal, and after the pump, the pipes after the respective zone valves for CH or HW also get hot when their service is selected on. So far, so normal.

However, individual radiators sometimes get hot, sometimes they don't. Nothing to do with their TRV or having the HW on or not - even with only CH selected and its feed pipe getting hot; sometimes some radiators will get hot, other times they won't, (TRV's set to max and house is freezing cold). Tonight, four radiators got hot but later went cold, (not because of the TRV's - the feed pipe to the rads went cold too, but still hot water from the boiler going to the main CH pipe via its zone valve).

There seems to be no rhyme or reason.

So, does this sound like a sludge blockage or an air lock? Why does the problem seem to move around the system? No air at the bleed screws of any radiator - just water flows out.

PS, there is some magnetite around where the FE feed joins the boiler feed pipe, and it is blocked - no water from the FE tank can get through. This will be addressed, but for now I put mains water into a drain cock until it came out of the FE overflow to make sure the system was full of water. But no magnetite in the individual radiator feeds.

The system I inherited when we bought the house is old, but I need to keep it going until the warmer weather, and cannot afford to break it open or decommission it just now if I can possibly help it.

Many thanks if you can help - I am running out of ideas and things to check.

 

[cross thread]

Remove the Trv heads and test it may be the they are out of calabration

 

[Elkato531]

Sort out the feed/vent connection. You say the cold feed is blocked but there will likely be restriction of the flow pipe as well. The magnetite build up can be quite solid so flushing is unlikely to shift it. Cutting out and replacing is required.

 

[feynman]

Some TRVs removed this morning and I will see what happens. I will also see if I can force out the airlocks if there are any.

I have been vibrating the pipework, (hammer drill set to hammer only with a plastic puck I made), where the magnetite is in the pipes, hoping I can at least get some flow and get some cleaner in. Or I might try some injecting cleaner into one of the radiators.

But failing that, tomorrow's job will probably be to cut out and replace. I really didn't want to have to do this during this very cold weather, since it will take me the best part of a day working in the restricted access, and will be messy, and no doubt, other problems will surface when I do so, but needs must. But why would a blockage cause radiators to sometimes heat up, sometimes not - surely they would not work at all if they had a blockage?

Tips for best way to cut pipes with restricted access? - I can't use a pipe cutter because there is no room for it to turn all around the pipe. Hacksaws jam on pipes, and I can't really get in there with a hacksaw anyway. Don't want to have to use the angle grinder owing to a lot of mess. Multi tool perhaps? If so, which one should I get?

 

[fixitflav]

Weird one this. Some radiators sometimes get warm sometimes they remain cold. (but not because of the TRV's or room stat, or boiler stat or boiler overheat stat - all those are normal and set appropriately).

We have tried every combination of CH and HW. Both zone valves move and work correctly when their respective thermostats demand heat.

The pump runs and has been bled of air, and I can hear that it is full of water internally.

The boiler feed pipe to the pump gets hot as normal, and after the pump, the pipes after the respective zone valves for CH or HW also get hot when their service is selected on. So far, so normal.

However, individual radiators sometimes get hot, sometimes they don't. Nothing to do with their TRV or having the HW on or not - even with only CH selected and its feed pipe getting hot; sometimes some radiators will get hot, other times they won't, (TRV's set to max and house is freezing cold). Tonight, four radiators got hot but later went cold, (not because of the TRV's - the feed pipe to the rads went cold too, but still hot water from the boiler going to the main CH pipe via its zone valve).

There seems to be no rhyme or reason.

So, does this sound like a sludge blockage or an air lock? Why does the problem seem to move around the system? No air at the bleed screws of any radiator - just water flows out.

PS, there is some magnetite around where the FE feed joins the boiler feed pipe, and it is blocked - no water from the FE tank can get through. This will be addressed, but for now I put mains water into a drain cock until it came out of the FE overflow to make sure the system was full of water. But no magnetite in the individual radiator feeds.

The system I inherited when we bought the house is old, but I need to keep it going until the warmer weather, and cannot afford to break it open or decommission it just now if I can possibly help it.

Many thanks if you can help - I am running out of ideas and things to check.

Do you get overpumping ie flow from the vent pipe over the F/E tank? That's usually a sign of a restriction between the open vent and cold feed connections.

 

[feynman]

No, but pump is downstream of the junction between the boiler flow and vent pipe, i.e. the pump is 'sucking' away from the overflow.

This is just really strange. For example one radiator comes on normally, but then goes cold after about 30 mins. Nothing else has changed. The boiler is still running, room stat still calling etc, and I have removed the TRV from that rad. I have also vibrated all the upstairs rads, and put pump on highest flow setting. But all rads except four are staying cold, and two that do come on initially go cold also.

????

 

[kidgreen61]

As said, you'll find blockage in or around cold feed, you can normally find it with a magnet.

 

[fixitflav]

No, but pump is downstream of the junction between the boiler flow and vent pipe, i.e. the pump is 'sucking' away from the overflow.

That's the most common set-up - boiler - open vent - cold feed - pump. A blockage between the open vent and the cold feed will still cause a flow into the circuit via the cold feed and out via the open vent. But it doesn't explain your symptoms.

 

[feynman]

This system goes : 28mm Boiler feed pipe, air separator with 22mm vent pipe, 28mm out of air separator, 28/15mm T off to FE cold feed, then into the pump. Cold feed certainly is blocked - magnetite all around the 15mm into the T junction, as found with a strong magnet.

Plumber's Merchants had never heard of Ferroquest, but they said Sentinel X800 is similar stuff. I am going to try to get some into the cold feed pipe from the FE tank - I think just a dribble of water is getting through under mains pressure, (I have plumbed the FE mains water feed into the CH system FE cold feed pipe, to try to clear the blockage, as suggested in FAQ's).

If the X800 opens up the FE cold feed pipe enough, I can put the rest of the X800 into the system and see if that buys me a couple of weeks until the warmer weather, after which I will cut it open if it is still not playing.

 

[conny]

I'm not a plumber so can't advise in any way except, a few weeks ago someone was talking about Sentinel X400 and Sentinel X800, and the general consensus was that you shouldn't use X800 and if you used X400 it should only be in the system for a few hours, not weeks.

It may be worth checking this out before you do some irreparable damage to your system.

 

[Elkato531]

If you have an air separator, it will, more than likely, be full of crap. Cut out and replace that whole section (without an air separator) before wasting time on any thing else. I woudn't want to be doing anything that would break up the blockage and send it into the system where it can get stuck somewhere else. After what you've already tried, I would, at the very least, be removing the pump head and cleaning out the impellor. X800 is aggressive but it won't shift hard deposited magnetite. It will destroy your pump if you don't flush it out completely after use. You clearly have very poor flow round the system which is showing up as only a few rads heating up. The water will take the easiest route and that route may change as water heats up and convection effects increase or decrease in different parts.