Advice on Cold and Warm radiators on second floor

[terryplumb]

Don't get bogged down with the positioning of the pipework to these rads ,fact is they have worked fine for years ,haven't they ? The lockshield valves on all your rads are used to basically create resistance to flow thru each rad. As the water is pumped around your CH it will always follow the path of least resistance. So if you have some rads that are not heating ,because the system is not balanced and no other issue , then the lockshields on those rads should be fully opened ,and the lockshields on rads that work fine would be closed down ,partially ,little by little. Thus having the effect of increasing resistance to flow thru those working OK ,and allowing increased flow thru the rads with fully open lockshields. That's the basic Jist of it .

 

[MeldrewsMate]

In my experience the effect of poor balancing is to give excess heat to the higher (2nd floor) rads at the expence of those on the ground floor. For those reasons I'll eliminate that as a main cause, and concentrate on the symptoms of poor heat flow to ALL loft rads.

My question(s) to you, Milleniumaire, is/are as follows:

Is there a thermostat on the second floor? I doubt it because you have been quite thorough in your description of the system, however there may be a second heating zone valve, perhaps concealed, somewhere near to where the loft pipework originated. It may have been wired into the existing heating thermostat's output. If you're competent with electrics have a look in the connection box for an extra (unexplained) core in the same terminal as the heating ZV's brown core....that is assuming you have 2 port valves controlling heating and hot water.
Consider the possibility that this notional extra zone valve has failed and remains closed, when all other rads are shut the extra flow pressure created causes it to be forced open slightly.

Try the 'all other valves closed' routine again, but with a quiet house LISTEN for the roar of water being forced through a restriction. Maybe in this way a concealed ZV can be located, and repaired.

'sjust a thought.

MM

 

[MeldrewsMate]

Oh, and on the subject of TRVs, Westherms are shi-ite. Draytons are good, but can stick down if left closed during the warmer months. The general rule is to OPEN all TRVs from Spring, and turn the heating OFF to ensure reliable operation in Autumn.

 

[Milleniumaire]

Hi MeldrewsMate, there is definitely no separate thermostat or zone valve for the loft radiators. They were added to the existing system 15 years ago when the loft extension was built and so controlled by the hall thermostat, like all other radiators in the house. 3 years ago, as part of a kitchen extension, underfloor heating was added, which has its own zone valve, however, the loft radiators were not affected by this and it was only a few months ago that I first noticed they weren't all heating up. Prior to this the loft was always too warm, with it being at the top of the house, so the TRV's on the two loft radiators were usually turned down.

I'll try to find time this week to turn off all the TRV's. Unfortunately it's back to work tomorrow after a week off

 

[Milleniumaire]

Spent a couple of hours today trying to troubleshoot the loft radiators, but don't feel I really got anywhere and I'm still as confused about the reason why they aren't heating up. Would really appreciate some guidance and ideas before I take the plunge and get a heating engineer in to have a look.

Turned off the TRV's of ALL the radiators in the house except one of the loft radiators; the one that never gets warm, despite being fitted with a new TRV. Turned up the radiator temperature setting on the boiler to full (75 degrees). Turned up the hall thermostat to 22 degrees (it's usually at 21 degrees). Turned down the kitchen thermostat (used by the kitchen underfloor heating) to 18 degrees (it's usually at 20 degrees). I have anologue thermostats on the flow and return pipes of the boiler and these are showing 48 degrees and 32 degrees respectively.

The result is that the loft radiator got slightly warm - not hot. In fact after 45 minutes some of the radiators around the house still felt warmer than the loft radiator although I could tell no water was getting into them. The feed pipe to the TRV's of most radiators was still warm/hot, so it's possible there was heat radiating through the pipework into the radiators?

Looking at the display on the Vaillant ecoTEC plus 637 system boiler, it was showing S.7 and the radiator symbol was flashing. S.7 means pump over run. I get the impression this is normal in the situation where the hot water is staying hot although it is dropping 16 degrees according to the thermostats, because it isn't radiating out through the radiators, so the boiler turns off, but continues to pump the still hot water around the system. I'm fairly sure the boiler has a built in diverter vavle. Is this likely to be in operation while I have the heating on full, but all radiators turned off (except one). If so, is this possibly the reason why the loft radiator isn't getting hot? How can I resolve this for testing?

 

[Milleniumaire]

Oops, while checking all the radiators and pipes again, noticed the radiator nearest to the boiler on the ground floor was still red hot despite the Danfoss TRV being fully closed. Messed around with it a bit and I think it has finally closed, but was clearly still allowing a trickle of water through before this.

Tested all radiators and they are now getting cold as are the flow and return pipes to each radiator. Radiator in the loft still only luke warm! Boiler still showing S.7.

 

[Milleniumaire]

It's now been three hours and the house is getting cold! All radiators are cold except the one in the loft, which is luke warm at best. Boiler is still showing S.7 and the flow and return thermostats are showing 55 degrees and 25 degrees respectively. Does this suggest hot water not actually being pumped around the system?
I've tried turning on the loft bathroom towel rail on its own, but this also only gets luke warm - probably not even that. So the problem towel rail and radiator are not heating up as expected.
If I turn on the working loft radiator this gets host pretty quickly so I guess hot water is being pushed around, but why isn't this registering on the return thermostat by the boiler? Turning on the working loft radiator seemed to cause the other loft radiator to get warmer, but the towel rail went cold. Both loft radiators seem to have hot and cool areas, with the bottom part of the radiator nearest the lock shield valve being the coolest. This is relative. On the working loft radiator the supply pipe, and most of the radiator is very hot, withe the exit area being only hot i.e. noticeable not as hot. This is even more obvious on the none-working radiator, which feels warm near the TRV and at the top of the radiator. I'm wondering if part of the radiator nearest the lock shield valve is possibly blocked with sludge. When I changed the TRV's on both loft radiators I noted sludge at the bottom of the radiator entrance and scraped it out, the best I could. As these loft radiators are the furthest from the boiler I assume there is more chance of sludge building in them as the water pressure won't be as high? I'm tempted to disconnect them and flush them through with a hose pipe outside.

 

[mcmoby69]

blocked flow or return maybe? are they piped in plastic or copper?
shut all your rads off. the ones you are having problems with. drain the rad into a bowl. once drained disconnect the flow rad valve from the rad tail. point into a bowl or bucket and slowly open it up, do you get a decent flow or just a drip when fully open?

do the same with the return on all problematic radiator

 

[Milleniumaire]

Hi mcmoby69, I'm fairly sure the loft radiators are piped in plastic, with copper tails to the radiators. These were added about 5 years after the house was built when we had the loft extension built. The rest of the house is all copper.
I assume if I'm going to do this with the three loft radiators (2 x radiators + 1 towel rail) I may as well part drain the CH down to the 1st floor? Then I can remove all three rads, take them outside and give the a good flush with a hose pipe? I should be able to see how much sludge is removed, if any.
Is it also possible some of the plastic loft piping is blocked or is this unlikely?

 

[Milleniumaire]

Ah, I think I have misread your post. You are asking me to check the flow of water out of the valve (TRV and lockshield) while there is still water in the CH pipes.

Unfortunately, emptying these radiators will be tricky as they don't have drain points, so I would have to do it through disconnecting the values, which could be messy, but I guess it's possible.

 

[mcmoby69]

Ah, I think I have misread your post. You are asking me to check the flow of water out of the valve (TRV and lockshield) while there is still water in the CH pipes.

Unfortunately, emptying these radiators will be tricky as they don't have drain points, so I would have to do it through disconnecting the values, which could be messy, but I guess it's possible.

yes.

yes through the valve tails.

yes it could be messy. bowl underneath tinfoil or plastic up behind the valve. patience young jedi. crack the nut and drain it. once the pressure is relieved undo the bleed vent and drain the rad completely.

welcome to the world of plumbing. there is a knack of doing everything, unfortunately it takes years of practise to get it right.

my money is on the plastic pipe being blocked.

 

[Milleniumaire]

Today I removed the affected radiator in the loft and then opened the valves on the pipework (one at a time). Although water flowed freely from the TRV valve, it was very slow and constant and I was able to fully open it. When I opened the lockshield valve water sprayed out and I was unable to fully open it due to the volume and force of the water.

What does this mean? Would you expect the water from both valves to have the same pressure? Does this suggest a blockage feeding the flow (TRV) - assuming of course this is the flow end! How can the pressure from both valves be so different?

I also took the radiator outside and thoroughly flushed it through. There was a lot of sludge in it. Tomorrow I'm going to do the same with the other radiator and possibly the towel rail if I get time. I've also purchased some Fernox F3 and plan to empty the system, then fill it up adding the F3. I'll leave this in for a few days, possibly a week, then empty/refill the system a couple of times. It will be interesting to see if this makes a difference to the pressure of water coming from the valves while the radiators are removed.

 

[Milleniumaire]

Tomorrow I'll attempt to identify the flow of the plastic pipes for the loft radiators. There's a crawl space in the eves on either side of the loft, so I think I should be able determine where the pipes are running. I guess I'm looking for the pipe (flow hopefully) that feeds the TRV on the affected radiator and trying to identify a point that might be blocked such as a tee, a bend or more likely an isolation valve?

 

[Milleniumaire]

Today, I removed the "working" radiator in the loft and cleaned it out in the garden. More sludge again . I then tested the pressure of each valve on each of the pipes entering the radiator. Same result as the "non-working" radiator and I didn't see any difference. The pipe connected to the TRV trickled water and I was able to fully open it without issue. The pipe connected to the lockshield valve gushed water out and I couldn't keep it open long due to the pressure and amount!

So, for both loft radiators, the TRV "supply" pipe seems to be under a lot less pressure than the lockshield "return" pipe. I say "supply" and "return" as this is the way I would have expected them to have been connected up, but I guess it should work equally as well if the "supply" connected to the lockshield and the "return" was on the TRV, wouldn't it?

Can someone please explain the difference in pressure between the TRV and lockshield valves. Is it possible this is simply down to the design of the valve or does this definitely reflect the pressure of water in the pipes?

Given that I saw similar pressures in the pipes to both radiators, I'm not sure this explains why one of the radiators heats up, but the other doesn't.

 

[dilalio]

The answer is sh!t in the system.
Deal with that and your problems will be resolved.
Then keep the system clean and well-maintained as it sounds like you have too many rads off of smaller bore trunks.