New radiator not getting hot

[Milleniumaire]

While redecorating a downstairs room I use for my office, I've taken the opportunity to replace the old single radiator with what is essentially a double (MHS Decoral 97 aluminium radiator, 657mm high x 900mm wide (11 sections)). Fortunately, the pipes from the floor below had lots of movement as they extend below the room into a void as the house was built on a concrete float, with the room floor sitting on large joists.

Having installed the radiator I was surprised to find it wasn't getting hot, just warm. I turned off all radiators in the house and turned up the boiler and was even more surprised it cooled down completely, along with the radiators that were turned off (obviously). Having turned on the downstairs radiators one at a time, I determined that the radiator in the downstairs toilet is somehow turning off the office radiator when it is turned off itself! However, even with all other radiators off, except the downstairs toilet and new office radiator, the new radiator is still not getting hot, while the downstairs toilet radiator is too hot to touch!

I turned all radiators back on and the amount of heat in the new radiator didn't really change. The house is 28 years old and this radiator piping has never been changed, so I can only assume it has always been like this! The reason for changing the office radiator was because the old one was too small for the size of the room and in the Winter months, the room was always on the cold side.

Regarding the new radiator, the (supply) pipe connected to the TRV is very hot and where the water enters the radiator is also relatively hot, but not as hot as the pipe. The radiator is warm at the top and cool at the bottom. The (return) pipe, connected to the lockshield valve is luke warm, with barely any heat. It's as though the hot water isn't adequately flowing through the radiator.

Any thoughts on what might be causing this?

Thanks.

 

[Johntheo5]

It's possible that it's installed inadvertently as a "one pipe" system, shut off both rad valves then open the vent fully, open the inlet (TRV) fully and note the intensity of the jet of water from the vent into a container, shut off the inlet and repeat by opening the return fully and compare both.

 

[CountryFan]

Designer radiator - I can’t get on the site using my dated iPad. However, you may have installed it the wrong orientation or may just need balancing, but if all others are hot and it doesn’t get hot with them turned off I’d say wrong way around.

 

[Milleniumaire]

Designer radiator - I can’t get on the site using my dated iPad. However, you may have installed it the wrong orientation or may just need balancing, but if all others are hot and it doesn’t get hot with them turned off I’d say wrong way around.

I didn't see anything in the instructions suggesting there was a right and a wrong way around. I installed a smaller, slightly different version a couple of years ago without issue and the TRV and lock shield are on the same sides.

 

[Milleniumaire]

It's possible that it's installed inadvertently as a "one pipe" system, shut off both rad valves then open the vent fully, open the inlet (TRV) fully and note the intensity of the jet of water from the vent into a container, shut off the inlet and repeat by opening the return fully and compare both.

Thanks for the suggestion. What should I expect and what is doing this showing?

 

[CountryFan]

I didn't see anything in the instructions suggesting there was a right and a wrong way around. I installed a smaller, slightly different version a couple of years ago without issue and the TRV and lock shield are on the same sides.

Managed to get on that site and managed to find instructions. Definitely a horizontal rad? Might just need balancing or there may be a restriction somewhere, which is what I think @Johntheo5 is asking.

 

[Milleniumaire]

Managed to get on that site and managed to find instructions. Definitely a horizontal rad? Might just need balancing or there may be a restriction somewhere, which is what I think @Johntheo5 is asking.

Thanks for checking the site. Yes, it's definitely a horizontal rad and I did see the installation requirements for vertical radiators, but they don't apply to mine.

 

[Johntheo5]

Thanks for the suggestion. What should I expect and what is doing this showing?

Do these tests with the boiler running, if the rad return is teed back into the main flow, then, when testing with the TRV shut and return + vent fully open, the return pipe should eventually get very hot, if pipework installed correctly then, there should be a stronger flow through the vent with the TRV+vent fully open. If a restriction in the return pipework then the flow through the vent should be very little?.

 

[Milleniumaire]

I "briefly" performed these test and the jet from the bleed valve appeared to be around the same pressure regardless of which valve was closed. I would have preferred to have done the tests for longer buy I needed my wife to hold the bucket and catch the water and she didn't have too much time. I was going to try again, but it hasn't happened yet.
While closing the TRV I noticed the pin was sticking, in fact after opening the valve, the radiator didn't warm up at all and I had to pull the pin and apply some lubricating spray. Comparing it to some other similar TRV's around the house I found one that was permanently open and didn't close!!! Both are Danfoss valves purchased in 2005, so now over 20 years old, not that they should fail!
I've therefore decided to replace the TRV AND the lockshield valve with Drayton valves, which I've also used elsewhere in the house and more recently. I plan to use an Arctic Hayes freezing kit, so fingers crossed! I used one of these many years ago with success, but I'm aware they are a bit hit and miss.

I've also done a bit more testing of the heating system/radiators and determine that the new office radiator getting warm isn't specific to the downstairs toilet radiator being on. If ALL the downstairs radiators are turned off, the office radiator stays cold, but if any of the downstairs radiators are on, the office radiator warms up. It's still not getting as hot as any of the other radiators and this is partly why I'm going to change the valves, just in case they are failing to fully open. If I don't change them, I will always wonder if I should have done!

One thing I also did was turn the circulating pump up to full speed (3rd setting of 3). With only the small toilet radiator on, all others in the house turned off, the office radiator actually got quite hot, but only on the side near the TRV (supply side) and the top. The bottom part of the radiator was warm and the return pipe and lockshield valve were barely warm, so clearly something is going on. Without being able to see all the piping under the house I may never get to the bottom of it. I can't believe this is an airlock preventing flow as it has been running with only 2 radiators and a full speed pump for over an hour, which I would have expected to clear any airlocks. Also, I had a constant stream of water from the bleed valve with the TRV closed and the lockshield (colder side) fully open.

It did remind me that the old radiator I removed was also regularly cooler towards the bottom but I had assumed that sludge may have built up over the last 28 years, which was part of the reason for changing it. I'm now wondering if the circulation issue was also a factor with that radiator. In fact I still have it and have considered putting it back on to test it and see if I get the same issue (after giving it a good flush through outside).

When the pump was on the high setting I could hear water flowing in the radiator and the smaller toilet radiator was the same, but with all other radiators, the return pipe was getting almost as hot as the supply pipe, which is what I would expect with the boiler and pump turned up, since hot water is being pushed around the system more quickly than it can radiate heat. On the new office radiator the return pipe never gets hot.

 

[Johntheo5]

Just had a scan through some fairly recent posts of yours and see it seems that you have a LLH??, if so, what is the boiler make/model/circ pump, internal/externally installed? and what is your secondary (rads etc) pump make/model?

Would definitely replace that TRV on that new rad.

 

[Milleniumaire]

The boiler is a Vaillant ecoTEC plus 637 with a built in pump and it was installed 15 years ago. The pump has never been replaced and I'm not sure what model it is as I'm "not allowed" to open up the boiler case as I'm not a heating engineer!
The external pump on the circulation side of the LLH (not the boiler side) is a Grundfos UPS3. This was installed in 2020 along with the LLH as part of adding a second UFH manifold to the system. The two UFH manifolds; one for the kitchen/dining/living area, and the other for the house bathroom, both have their own pumps. The following is a diagrm of the full system, although the order in which the radiators are shown connected may not be correct, apart from the loft as I did a lot of work getting a botched install by a loft extension company to work properly.

 

[Milleniumaire]

I meant to include in my earlier post that I wouldn't have thought my issue was due to unbalanced radiators, since turning the radiators off doesn't seem to make that much difference.

 

[Johntheo5]

The LLH makes your trouble shooting easier as you can rule out boiler HEX fouling as playing any part of the problem.
Also, the UPS3 is a giant of a 6M (6.4M) circ pump at 60W as against 40W for most of the "others". You can see, below that it will circulate over 20LPM (1.2m3/hr) and still maintain a > 6M head on CC3 and will circulate over 18.0LPM at > a 5M head on CC2, so bags of circulating head there so definitely looks like a piping problem or the "new rad" problem, anyhow install that new TRV and take it from there