Gravity feed to bathroom rad dissappointing

[MarkTravis]

I have just purchased a house builtin the 1920's. The CH system was apparently installed in 1987 - although a new-ish boiler since then (Ideal RS55). The system works like this: There is a header tank in the loft, the main radiators are pumped but the hot water and bathroom radiator are on a gravity feed. There is no thermostat on the hot water tank. The programmer only allows the heating to be on if the water is also on (fair enough!).

This gravity feed to the bathroom radiator is the pain in my butt right now. The original radiator was dented and corroded at the valves, it was a very small rad 500x400, so I swapped it out for one which is slightly bigger at 700x500. The problem is that whilst the ugly, leaky old radiator got reasonably warm, the nice new radiator is now luke warm. I have bled and bled but to no avail. However, if I switch the heating to the rest of the house off (i.e. hot water only on) it gets very warm indeed.

Example: bedroom 3 radiator gets to 45c degrees, the bathroom 31c - big difference

This suggests to me that the gravity feed to the hotwater & radiator is not 'strong' enough (if that's the right word) to cope with this slightly bigger radiator - so what are my options?

In a way I rather like the idea of this radiator coming on with the water because you might need bathroom heating in early/late summer but not the full house central heating, so I don't want to connect the radiator to a primary flow unless that's my only option.

 

[MarkTravis]

What? nobody got any ideas?
Surely not!

 

[Nige F]

They are all out @ work still

 

[ChrisOxford]

I'd be interested to hear what people have to suggest too.

My parents had two towel rails plumbed in the same way in their old house (1930s build with 1960s plumbing and newish boiler). They suddenly stopped working well and more than one plumber was unable to help.

 

[Whitespirit66]

What valves have you got on the rad?

 

[MarkTravis]

What valves have you got on the rad?

I have no idea what make or model, they were sold to me by the guy at the plumbcentre. They connect to standard 15mm tails which come off a 22mm pipe.

I currently have both values fully open I just did a temperature check and the flow end is reading 34c whilst the return is 27c.

 

[MarkTravis]

....So do the valves mean anything?

 

[Nige F]

What valves have you got on the rad?

What valves did you have on the rad that worked ? - I`d want 3/4 valves and tappings and a rad with end tappings not the modern back tappings

 

[MarkTravis]

What valves have you got on the rad?

What valves did you have on the rad that worked ? - I`d want 3/4 valves and tappings and a rad with end tappings not the modern back tappings

The original radiator had the same (similar) valves as the new radiator. The valves do stick out from the side of the radiator which is a Stelrad.
You are implying that the copper pipework to the rad should be 22mm with 3/4(22mm?) valves - I can't see those listed anywhere BTW. Is changing that pipework my only option?

 

[Nige F]

OK , pipes and valves pretty much the same - do the connections to the rad have a kind of bulbous thing they screw in that is attached to the back of the rad if it`s a single panel ? - that`s what I mean by a back tapping very common on new rads . If it was plumbed in 22mm. it would fly round , but realistically not worth the hassle - I have a feeling the restriction is in the rad tapping

 

[45yearsagasman]

IMO the construction of modern rads does not lend itself to gravity circulation. Older rads had bigger waterways and less resistance to flow.
New rads are not designed with gravity in mind. Maybe a visit to a reclaim yard will produce an older style rad. Just a thought.

 

[ChrisOxford]

The system I referred to above had 22mm pipes (and the equivalent in iron in places), and had two huge (and ancient) chromed towel rails plumbed in series rather than a rad, which makes sense in view of that Nige and 45yearsagasman have said.

 

[MarkTravis]

Well, the old radiator and the new are pretty much visually identical. I notice that the hole that the valve screws into was the same as the old radiator - simply because I did think I'd re-use the valves off that but when I saw the sludge, thought better of it and flushed the system again!

There is no 'bulbus' connection (I know what you mean by that) the only difference between the old and new radiator is the size....and the fact that the new one should have a much better, unrestricted flow!

 

[DeltaT2]

I have just purchased a house builtin the 1920's. The CH system was apparently installed in 1987 - although a new-ish boiler since then (Ideal RS55). The system works like this: There is a header tank in the loft, the main radiators are pumped but the hot water and bathroom radiator are on a gravity feed. There is no thermostat on the hot water tank. The programmer only allows the heating to be on if the water is also on (fair enough!).

This gravity feed to the bathroom radiator is the pain in my butt right now. The original radiator was dented and corroded at the valves, it was a very small rad 500x400, so I swapped it out for one which is slightly bigger at 700x500. The problem is that whilst the ugly, leaky old radiator got reasonably warm, the nice new radiator is now luke warm. I have bled and bled but to no avail. However, if I switch the heating to the rest of the house off (i.e. hot water only on) it gets very warm indeed.

Example: bedroom 3 radiator gets to 45c degrees, the bathroom 31c - big difference

This suggests to me that the gravity feed to the hotwater & radiator is not 'strong' enough (if that's the right word) to cope with this slightly bigger radiator - so what are my options?

In a way I rather like the idea of this radiator coming on with the water because you might need bathroom heating in early/late summer but not the full house central heating, so I don't want to connect the radiator to a primary flow unless that's my only option.

With every gravity system, the rising hot water in the Flow is the circulation power for the Return. Is your Hot Water cylinder getting hot enough? Have you altered the F&R pipes to the radiator in any way - like extra elbows etc?? Is your boiler thermostat out of calibration??
Why not post up a wee rough sketch of your system, a picture is better than a 1000 words, for the hard of thinking on DIYdoughnuts............

 

[45yearsagasman]

for the hard of thinking on DIYdoughnuts.

I resemble that remark