radiator only heats up when other rads off. Please help!

[jodaniel1]

Apologies in advance for the long post, but I want to outline everything I've tried so far to give a full picture.

The radiator furthest from the boiler (Gas Boiler; Ideal Concord WRS355A) only heats up if any 2 or 3 other radiators are turned off. Even then it gets warm but not really hot. When all the other rads are on, the pipe to this rad is hot til a couple of feet from the rad, but not all the way. It has been like this since I moved in. I have tried the following so far:
Bled the radiators; Balanced the radiators; - made no difference.
I then called in a plumber who undid the pipe to the radiator. Some sludge came out but then clear water, so he confirmed there was no blockage to the radiator. He suggested I change the radiator as it may be blocked. So I bought a new rad, had it changed (by a different plumber)... no difference. All this proves is the problem wasn't the rad in the first place!

The guy who changed the rad suggested I try power flushing, as there might be a blockage in the pipes, but couldn't be sure it would work.
I am sceptical about this, is power flushing a waste of time? I can't afford to keep spending money that doesn't fix the problem! Surely if there was a blockage the rad wouldn't heat up even when other rads are off?
Both plumbers said the pump (Grundfos 15-50) is old but working fine. I feel like I've been ripped off; have paid good money to 2 different plumbers, paid for a new rad and still no joy!

Please help! The room affected is the biggest room in the house, and if I can't heat it the whole house suffers!
Thank you.

 

[D_Hailsham]

Balanced the radiators; - made no difference.

Definitely sound like a balancing problem.

Is this a new problem, i.e the rad used to get hot but now it does not, or have you always had it?

Do you have TRVs on the rads?

What procedure did you follow when balancing the rads?

 

[jodaniel1]

I have always had the same problem since I moved in, but the room hasn't been in use for various reasons. I now need to use it so need to heat it!

Yes there are TRV's on all the rads, and a new one on the new rad which still won't heat up.

When balancing the rads I got pipe thermometers, followed the instructions in my trusty Readers Digest DIY manual, and went round the rads in the order they heat up. The problem rad is the one furthest from the boiler, and its lockshield valve is fully open....

 

[superdupergasman]

What speed is the pump on?? there is a little white adjustment knob on the side that will tell you.

Some pumps slow down with age, so before you get cutting out pipework looking for a restriction in the system, I would get a new shiney Grundfos pump in there; maybe even uprate to a 15/60 if its supplying a large system.

 

[jodaniel1]

What speed is the pump on??

The pump is on max speed.
I don't think I have the expertise to change the pump myself, so will have to get someone in if I try that. I'm wary because I don't have a plumber I've known for years who I can trust. I just have to pick someone out of the phone book, and that hasn't gone well so far. I've already spent over £300 on the initial advice and buying and chainging the radiator, so want to be sure that whatever I do next will work...

 

[superdupergasman]

How about getting BG in for a fixed price repair. for £170 they can change the pump.

Speak nice to the Engineer and they will give you some advice.

 

[jodaniel1]

How about getting BG in for a fixed price repair. for £170 they can change the pump.

Thanks, I didn't know they did that...

 

[D_Hailsham]

Yes there are TRV's on all the rads, and a new one on the new rad which still won't heat up.

I hope you do not have a TRV on the rad where the wall thermostat is located. If you do, you should either replace it with a standard valve or take the top off, so the valve is fully open.

Do you have a fully pumped system (Y or S plan) or is the HW on gravity circulation?
If you have S-plan, do you have a bypass valve - manual or automatic?

When balancing the rads I got pipe thermometers, followed the instructions in my trusty Readers Digest DIY manual, and went round the rads in the order they heat up.

Pipe thermometers are useful, but they are very slow reacting to temperature changes; so balancing takes a long time -which you will have found out by now.

Did the RD Manual take TRV's into account in their instructions? I bet they didn't.

The problem rad is the one furthest from the boiler, and its lockshield valve is fully open

If the LS valve is fully open, it's not doing anything. I suppose the RD Manual says that the early valves will be partly closed and the end ones open. Wrong. On a properly balanced system, the valves will be open no more than one and a half turns.

Balancing procedure:
Note change

1. Make sure HW is turned off
2. Open all LS valves fully; remove all TRV heads and open all manual valves fully.
3. Turn the boiler temp to max and bring system up to temperature.
4. Adjust the bypass (if fitted) as per mfr instructions
5. measure the temperature differences between the flow and return pipes at the boiler. For your boiler, it should be 11°C. If the temperature is not right, you need to adjust you pump speed (higher speed gives smaller difference and vice versa). Set the speed to give as near a difference as possible.
6. Turn the boiler off.
7. Close all lockshield valves
8. Restart boiler
9. Attach the pipe thermometers to the rad nearest the boiler and open the LS valve a quarter turn
10. Wait until temperature has stabilised on the two thermometers. If the difference is smaller than that at the boiler, close the LS valve a fraction, or vice versa. Wait until the temp has stabilised and check again.
11. When you are happy with the first rad, move on to the next.
12. When you have reached the last rad, check the boiler temp difference and adjust pump speed if necessary.
13. Go back to the first rad and test it is still giving the correct difference
14. And so on, going round and checking the temperature difference until they are all as near 11°C as you can make them. Don't expect perfection

A very small change in amount the LS valve is open can have a considerable effect on the temperature difference. Because of the way LS valve are constructed, it is virtually fully open when it is one and a half turns open. So most adjustment will be within one turn from closed.

 

[MANDATE]

Hi Jodaniel. My son had same problem, wasted a couple of hours removing and cleaning radiator and nothing changed.
Found a by pass pipe with valve that was fully open. Pretty sure this was the cause. Water will take the easiest route, as it would rather go through the by pass than travel and pass through furthest radiator. Closed valve and radiator got warm for the first time in ages. but it did not match other radiator in same room (opposite wall)
Pump sounded a bit noisy and decided to remove it for examination.
The inlet and outlet orifaces were almost blocked off with black deposit sludge.( down to a diam. of approx 5mm).
Fitted new pump and isolating valves ( 1 isolating valve could not be closed, drain down) and problem solved.

 

[Agile]

I am sorry you have been the victim of rather incompetent plumbers!

You have been asked about your hot water heating and the controls. We would like to know if you have a mid position valve or two two port valves or a gravity hot water circuit.

Its possible that the hot water cylinder is never being turned off and the flow through it is too high to enable the heating to work properly.

I diagnosed a problem like that and told the owner what her plumber needed to do.

The plumber evidently was not clever enough to understand what I had asked him to do so he had to telephone to ask me why. I explained and he was happy with my explanation, fitted the lockshield to the hot water cylinder and set it open 1 turn and then the rads worked perfectly.

Tony

 

[Macgasman]

What do you mean by adding a lockshield to a hot water cylinder?

How do you do that? Do you mean a tapstat?

 

[jodaniel1]

I hope you do not have a TRV on the rad where the wall thermostat is located.
A; There is no wall thermostat, in the house, only the TRV's. It's a weird system,
Q: Do you have a fully pumped system (Y or S plan) or is the HW on gravity circulation?
If you have S-plan, do you have a bypass valve - manual or automatic?

A: not sure, how would I tell? The HW cylinder has a TRV attached which controls how quickly the water heats up. I keep the HW turned off most of the time, or keep it on very low.

When balancing the rads I got pipe thermometers, followed

No, the RD manual didn't take TRV's into account!

Quote: I suppose the RD Manual says that the early valves will be partly closed and the end ones open.

A; That's exactly what it said, but I'll try your procedure at the weekend.
Thanks for all the tips...

 

[jodaniel1]

You have been asked about your hot water heating and the controls. We would like to know if you have a mid position valve or two two port valves or a gravity hot water circuit. Tony

I might sound dim but I don't know! There is no separate HW setting as such on my heating timer. The HW is turned on via a TRV attached to the cylinder. I know from expreience that having the HW on anywhere near full reduces the heat to the rads, so the HW is usually off or on the bare minimum setting. If I want hot water fast I turn the rads off with the isolator valve that is my 'summer setting',... does any of this make any sense???

 

[D_Hailsham]

A; There is no wall thermostat, in the house, only the TRV's.

You need to get one fitted. TRVs do not know when to turn the boiler off, so it will keep running until the boiler thermostat turns it off. This wastes gas

Q: Do you have a fully pumped system (Y or S plan) or is the HW on gravity circulation?
If you have S-plan, do you have a bypass valve - manual or automatic?

]A: not sure, how would I tell? The HW cylinder has a TRV attached which controls how quickly the water heats up. I keep the HW turned off most of the time, or keep it on very low.

What make/model is the TRV on the HW cylinder?

This is a pump:

View media item 802
If you have motorized valves they will look like one of these:
View media item 800 View media item 801

No, the RD manual didn't take TRV's into account!

I suppose the RD Manual says that the early valves will be partly closed and the end ones open.

A; That's exactly what it said, but I'll try your procedure at the weekend.
Thanks for all the tips...

I thought as much. I made the mistake of buying a RD Manual years ago - just for general DIY advice - and have frequently found it unreliable.

 

[jodaniel1]

A; There is no wall thermostat, in the house, only the TRV's.

You need to get one fitted.

I have thought about getting an RF roomstat because it saves the hassle of so much wiring, but I'll tackle that another time once this problem is fixed!

[/quote]
What make/model is the TRV on the HW cylinder?

It's a Drayton, can't see a model; it's just a dead basic TRV.

If you have motorized valves they will look like one of these:

I don't recognise the motorised valves at all, so it the HW must be gravity fed.

I will try the balancing at the weekend and report how it goes...