Radiator fails to warm up


Postby Longbow archer » Thu Oct 18, 2007 1:09 pm

Hello everyone.

I know this topic is often repeated on the forum, but after viewing some of the replies, I still have questions as to why my bedroom radiator will not warm up....

Heating system = semi-gravity running off a back boiler (probably around 20 years old), large hot water cylinder, plastic feed and expansion tank. Piping to radiators is larger bore downstairs, smaller bore upstairs. I apologise for the non-technicality here!

Problem: bedroom radiator barely gets warm (this morning I had to switch on the portable fan heater after a pretty cold night).

Firstly, I cannot see any visible leaks (i.e. no puddles of water anywhere in the house). Air gets trapped in the 'problem' radiator all the time. In fact, in order to get the tiniest bit of warmth through it, I have to bleed it. I am doing this every day (with the pump off). The radiator inlet pipe slowly warms but doesn't get anywhere near hot. The outlet pipe stays very cold. Over a period of hours, the radiator only warms very slightly. Sometimes this warmth will tend to be at the bottom of the radiator, at others it will be towards the top.

All of the other radiators are nice and hot (especially so now since a double radiator downstairs has been flushed to remove approximately half a tonne of gunk!) and do not need bleeding. The other two radiators upstairs are fine.

None of the radiators have modern TRVs. Instead they have older simple valves. Two of the radiators (one in the study and the 'problem' one) have identical valves at either end with spindles exposed and no cover to turn in order to open and close the valves. The radiator in the study obviously has the valves open at either end as water is passing through OK and is hot. Could it be that on the 'problem' radiator, the valves are not fully open? N.B. I've already broken the top 1 cm of the spindle on one side!!!

I've checked that the ball in the feed and expansion tank is elevated a few inches above the outlet pipe - all seems to be fine there.

A friend has suggested that I turn all the radiators off that I can and force the system to pump through the study and 'problem' radiators to see if that removes a blockage/airlock. Is this likely to help? Alternatively, could it be that the pump is not turned up high enough (I don't know how to get to it)?

Should I replace all of the valves just in case? Can I establish if one valve is leaking? N.B. At present I do not have any drain valves fitted.

I apologise for the rambling description but have put it all here in the hope that someone out there may be able to offer some advice on what to do next (and before winter sets in!).

Thanks,

Sarah
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Postby The Heating Doctor » Sun Oct 21, 2007 12:01 am

Where to begin?

1) Yes you should get TRV's fitted and as you are renewing these you should renew the lockshield valves. Fit the downstairs radiators with lockshield drain off valves. A pack consisting of a TRV & Lockshield drainoff will cost around £9 with vat and a TRV & lockshield pack around £8 with vat. They will save you more than this on your gas bill in about 24 mounths.

2) When you removed the gunk from the flushed radiator did you add an inhibitor to the system? Can the problem radiator be gunked up? What colour is the water when you bled this radiator?

3) Yes it could be the pump running out of steam to feed the last radiator, so you need to find it and check to see if the pump speed can be changed.
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Postby Longbow archer » Mon Oct 22, 2007 8:28 am

Heating Doctor,

Many thanks for the info. As for your suggestions/questions:

(1) Will do as you suggest and fit TRVs, new lockshields and drain valves where appropriate.

(2) We didn't add any inhibitor to the system this time. We might as well do this when we drain the whole system down to fit the new valves. How much inhibitor would we need to buy?

We're not sure if the problem radiator is gunked up. When bleeding it, the water initially comes out containing a relatively small amount of black residue. If bled longer to deliberately get more water out, the water is slightly brown in colour.

(3) We are guessing that the pump is located with the boiler, behind the gas fire in the living room...... the hunt continues.

Sounds like we've got some work to do!
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Postby The Heating Doctor » Mon Oct 22, 2007 10:03 pm

Sounds like you do. The amount of inhibitor required depends on the make you purchase, check out dosing qty on the manufacturers packaging. Black sludge in a CH system is never good, you may want to install a Magnaclean or Fernox Boiler Buddy to help prolong the life of your system, removes magnetite, rust and magnetic materials from heating systems to sub-micron level to prevent further damage to the system components.
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Postby Longbow archer » Tue Oct 23, 2007 9:13 am

Thanks again for the advice.

Due to recently paying out for my house to be re-wired, I can't afford to go at this hammer and tongs right now. I'm hoping that if I initially drain down the system, fit new valves etc. and add inhibitor to the system then that at least will afford some protection.

I'd found the Magnaclean website a while back but had not heard of the Fernox Boiler Buddy, so thanks for giving me 2 options to consider. When I get the boiler serviced, would it be appropriate to ask the heating engineer to install one of these devices, i.e. are they likely to oblige?
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Postby The Heating Doctor » Tue Oct 23, 2007 10:46 pm

I would imagine your service engineer would not have a problem fitting one. Just ask before hand so he can book the correct amount of time to the job or he may have prebooked other appointments after your service and not have time to install on the same visit as your service. Feed back from customers re these units is that they tend to prefer the Magnaclean as by using the isolating valves they can unscrew the chamber, clean off the magnet and fill the magnacleans chamber full of inhibitor before rescrewing the chamber back on, opening the valves, switch on the pump and the inhibitor is flushed into the system. The chamber can be filled as many times as is required to get the correct amount of inhibitor in to the system. Quick and easy with out the need for adaptors or crawling in to roof space if on a open vent system.
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Postby Longbow archer » Wed Oct 24, 2007 8:57 am

Thanks again for replying to my post.

I still have the cold bedroom radiator to deal with. As mentioned before, the two valves do not have covers (they don't have grubb screws on the tops of the spindles in order to take covers that are turnable). All they have is a spindle with no dimple in the top. I suspect that the inlet valve is only minimally open whilst the outlet valve is virtually closed. Is it safe to carefully try and open the valves up with a pair of molegrips (having already sprayed with WD40 in anticipation of this)? A silly question perhaps, but I don't want to give myself more problems!
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Postby The Heating Doctor » Wed Oct 24, 2007 4:43 pm

If careful should not be a problem. will the caps from the other radiators not fit?
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Postby Longbow archer » Thu Oct 25, 2007 8:20 am

Unfortunately not. All the other rads (bar one other) have spindles with dimples on the top in which the cover is attached to the spindle by a grubb screw. [/img]
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Postby elscripto » Fri Oct 26, 2007 8:41 am

I agree with what has been said so far but I had one other thought. It sounds like the system maybe isn't properly balanced. In other words, one valve on each radiator should be only partly open so that each radiator gets a share of the hot water. If you have one or more radiators fully open, the water will take that route and the radiators at the far end of the system will never get hot. Try what your friend suggested and turn the other radiators off to see if that makes the problem radiator get hot.

Assuming that you haven't got TRVs, each radiator should have one valve with a head that turns the spindle and one with a cover over the spindle (lockshield) - underneath they are both the same. The lockshield should be adjusted to balance the system. You can be technical about this and get pipe thermometers and adjust for 1C temperature drop on each radiator. Or you can open the lockshield valve a quarter turn on the rad nearest the boiler, open the next one half a turn and so on until you get to the furthest rad. After an hour or two, if any rads still seem too cold, you can open them an extra quarter turn at a time until they get hot.

Hopefully, you will be able to get enough heat to keep going until you can afford to replace the system.
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Postby Longbow archer » Mon Oct 29, 2007 9:43 am

Many thanks for your suggestion elscripto.

I'm looking to buy new valves for all the radiators (TRVs and new lockshields, two with drain valves for downstairs) and with help, will be draining the system down and fitting them soon. I'll try your method when the new valves are newly installed.

By the way, I still couldn't get the spindles undone on the cold radiator, so will just have to wait until the appointed day comes for changing all the rad valves!

Thanks again.
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Postby Longbow archer » Tue Nov 27, 2007 1:34 pm

OK, it's a month on from my last post and I thought I'd bring you up to date with the heating in my house (for the Heating Doctor and elscripto in particular, who were full of helpful advice).

This weekend we drained the system, flushing out all of the radiators in the process. All of them had sludge in (of varying colours). The one that had always been a problem in the bedroom as it never even warmed slightly, was absolutely full of gunk and the valves were only half open (and stuck there). Therefore, it didn't stand a chance of receiving any water.

TRVs and drain-off lockshields have been fitted to all bar one of the radiators and a new double radiator has replaced an old manky single one in the bathroom that had far too low a BTU rating. We've had to put in some nifty extra small lengths of pipe in order to cope with the extra distance required for the drain-offs and a few other jobs have been a bit fiddly but all is looking good so far.

Tonight we're adding Fernox cleaner and re-filling the system!!!!!!! If all is well, the system will be drained down again in a few days to remove any more gunk cleaned out from the pipes, boiler etc. and inhibitor added.

All being well, I'm looking forward to having my heating back on again tonight!
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