Gravity fed radiator..

Jass · 29 Aug 2006

I hope nobody minds if I jump onto the back of this thread, but I notice that there are some knowledgeable people involved in the topic.

I also have a gravity radiator. This is on a gas fired back boiler system (previously solid fuel), and my problem is that the rad struggles to get hot at all!
The rad is upstairs in the bathroom, has standard valve at one end and lockshield at the other, both left fully open.
The rad 'tries' to get hot and you can feel the warmth starting to come through but then it ebbs away even though the system remains on - in fact it is just like the tide coming in and going out - but very rarely does it get hot and stay hot.

Any thoughts on the cause and remedy would be greatly appreciated - especially with Winter (and thoughts of an icy bathroom) looming.

Jass.

doitall · 29 Aug 2006

Air lock in the return, but more likely the radiator is sludged up and wants a good flush.

3GHOTHEAD · 29 Aug 2006

doitall said:
The pressure relief/safety valve is an important part.

Check with the appliance manufacturer for the pressure, possibly 6 bar.

Hi doitall thanks for the endorcement . here

Jass · 30 Aug 2006

Thanks 'doitall', but I'm not sure that slidge is the problem. On the occasions the rad does get hot it happens quite quickly and is uniformly hot top to bottom.

How would I deal with an 'airlock in the return'?

Thanks in advance.

Jass.[/quote]

doitall · 30 Aug 2006

If the rad gets hot top to bottom sometimes, I think it's time for a sketch, email in my profile

Softus · 30 Aug 2006

Jass said:
I hope nobody minds if I jump onto the back of this thread

Well, you are hijacking and you should create a new topic.

Any thoughts on the cause

I don't see how it can be an air lock.

This kind of problem is usually down to balancing, but you can't balance it because the rad isn't on the same circuit as the other rads.

Does it get hot when the CH is switched off?
Has the problem started only since your boiler was replaced?
Was any pipework changed, e.g. bypass?

Oh, and be very wary of diagrams that doitall sends you in private - he has very unconventional (i.e. wrong) ideas about water pressure and flow.

Jass · 30 Aug 2006

Thanks for the quick response 'doitall'.
I don't think there's much more I can add.
It's a single 3ft rad in the bathroom; entry and exit valves are both at the bottom; at each end a 6 inch length of pipe descends into the floor and (I think) then must run horizontally under the floor to where the water heating coil rises into the airing cupboard (although any juction is hidden beneath the flooring); seems to be no problem with water flow as water exits freely when bleed valve is opened.
Rad can be nice and hot one minute and then go cold even though the system is still running.
This was never a problem when the system was solid fuel; it has only become apparent after changing to gas.

Could this just be a weakness of a gas fired gravity system, or is there something fundamentally wrong?

Jass.

Jass · 30 Aug 2006

Softus,

My apologies for breaching protocol, but thanks for the response.

No pipework was changed; it was just a straight swap - out with the soilid fuel boiler, in with the gas boiler. As far as I can say, that was when the problem started.
Your question relating to CH is interesting; I think that it seems worse when the CH is on, as it is more noticeable on cold days when the CH pump is running, but the problem is by no means limited to such times.

Jass.

Softus · 30 Aug 2006

Hard one to diagnose without knowing the pipe layout, but one strong possbility is that you have a blockage.

For example, when the boiler was replaced, it's inconceivable that the primary pipework would not have to have been modified to suit the inlets/outlets on the new gas appliance. This means disturbing pipework that would be likely to contain bits of detritus that had accumulated over the years. Another source of crud is the F&E cistern - if the system was drained without first empyting this, then any solids would be drawn into the system.

If the system wasn't flushed out, before installing the new boiler, then any muck is capable of lodging, and likely to lodge, in the smaller gaps, which will be boiler heat exchanger pathways, 15mm pipework to the rad and the 15mm rad valves.

Did the installer thoroughly clean out the F&E cistern?
Did he flush the system?
Did he add a chemical inhibitor to the final fill?

If you can't answer "yes" to ALL of those three, then if I were you I'd drain the system and flush it out. I'd use the opportunity to remove the troublesome rad and flush that out too. And add an inhibitor when refilling.

One other possibility is that the cold feed is partially blocked, sometimes starving the radiator of water and at other times not.

The test for this is to drain water from the system equal in volume to twice the current contents of the F&E cistern. Make sure that the boiler and pump can't operate, then shut off the supply to the F&E first (or tie up the float arm). Then do the partial draining, then refill while watching the behaviour in the cistern. If water readily leaves the outlet, then no blockage. If it doesn't, or if the cistern doesn't empty when draining, then you have a blocked cold feed.

doitall · 30 Aug 2006

Softus said:
Oh, and be very wary of diagrams that doitall sends you in private - he has very unconventional (i.e. wrong) ideas about water pressure and flow.

Unconventional, maybe,

Just remember water doesn't always do what you expect.

Softus said:
Hard one to diagnose without knowing the pipe layout, but one strong possbility is that you have a blockage.

Ok, so he can send the drawing to you instead, not that it will do any good.

Ask the poster what boiler has been installed (make and model).

Keep guessing.

Softus · 30 Aug 2006

doitall said:
Unconventional, maybe,

And wrong, certainly.

Just remember water doesn't always do what you expect.

Not so - it's what you expect water to do that doesn't always happen.

Ok, so he can send the drawing to you instead, not that it will do any good.

I haven't asked for a drawing, and I don't want one. If the poster has one then it should be put on the forum for all to see and comment on.

Ask the poster what boiler has been installed (make and model).

If it becomes relevant then I will. If you want to know, then I suggest that you ask. If you already know, and are withholding the information because you think it gives you some advantage, then you are a fool.

Keep guessing.

<insult removed>

If you believe that you know the cause of the problem, and/or the remedy, but are not publishing the information, then you're preventing other punters from benefitting from the knowledge, which is in conflict with the ethos of the forum.

MOD 2

calm it down (both of you )

doitall · 30 Aug 2006

If you believe that you know the cause of the problem, and/or the remedy, but are not publishing the information, then you're preventing other punters from benefitting from the knowledge, which is in conflict with the those of the forum.

No, I don't know what boiler has been fitted, or anything about the system.

Why should I make stupid suggestions just for you to rubbish the idea.

If Jass sends me the information and it cures the problem, he can tell you afterwards.

Softus · 30 Aug 2006

doitall said:
No, I don't know what boiler has been fitted, or anything about the system.

Well then, the reason for you posting on this topic is a mystery, seeing as you aren't helping anyone.

Why should I make stupid suggestions just for you to rubbish the idea? [Ed - punctuation corrected]

I dunno? For the same reason that you make stupid suggestions elsewhere, I guess.

If Jass sends me the information and it cures the problem, he can tell you afterwards.

See ya.

Jass · 30 Aug 2006

Softus said:
Did the installer thoroughly clean out the F&E cistern?
Did he flush the system?
Did he add a chemical inhibitor to the final fill?

Thanks for the interest. For a time, the forum seemed to be heating up much better than my bathroom rad!! Sorry if I set something off.

Softus, I am afraid I believe that the answer is in the negative to all three questions. I'm not aware that any of those things was done.
There is no separate F&E tank, etc.; all water - hot and cold - are encased in a self-contained 'ELSON' tank which is not easy to access.
The upper front portion of this is a small cold tank with a ball-float valve, and this part of the set-up I can see into with the aid of a torch and a mirror!
Could this be functioning as the F&E If so, then it does seem to be quite clean and free of debris.
When you recommend flushing the system, is this just with clean water or do I need at this point to get professional help?

Thanks again.

Jass.

Softus · 30 Aug 2006

Jass said:
Thanks for the interest. For a time, the forum seemed to be heating up much better than my bathroom rad!! Sorry if I set something off.

Not your fault, so please don't feel sorry.

Softus, I am afraid I believe that the answer is in the negative to all three questions. I'm not aware that any of those things was done.

That's a pity. If the installer was thorough then there will be label recording the date that an inhibitor was added, if it was. You might consider asking them directly whether or not they did.

There is no separate F&E tank, etc.; all water - hot and cold - are encased in a self-contained 'ELSON' tank which is not easy to access.
The upper front portion of this is a small cold tank with a ball-float valve, and this part of the set-up I can see into with the aid of a torch and a mirror!
Could this be functioning as the F&E If so, then it does seem to be quite clean and free of debris.

Yes - this is the F&E.

When you recommend flushing the system, is this just with clean water or do I need at this point to get professional help?

It depends on the amount of rust and sludge.

I would start by removing the guilty rad and flushing out with clean water. until clean. If what comes out is very gooey, then I would progress to cleaning the system with a product such as Sentinel X400 or Fernox Supafloc. You can leave this in for a few days, then drain again and flush through, then add X100 or MB-1 on the refill.

There are lots of topics that cover flushing out methods - I suggest that you have a look and then come back here if you can't find the information you need.

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Gravity fed radiator..

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