Old Style Cast Iron Rads hot at top cold / cool at bottom

[RonG]

Hi All, First post on the forum and hope its a good'n !

Story goes like this....

I salavaged a number of Ideal standard 4 column cast iron rads from a warehouse a few years ago, brought them home, removed all the old fittings, flushed em out with a hose in the back yard till water ran clear and then fitted them up with reducers to connect them to modern 15mm pipe and rad valves.

Type of rad can be seen here -

I removed the existing rads and fitted these up in their place with minimal alteration to the existing pipework.

I fitted the valves so that on one side of the rad the valve is on top and on the other side the valve is on the bottom.

I then fitted a Vaillent 832 Ecomax to drive the system.

Now that we have had a couple of colder than usual winters I am beggining to question the efficiency of the system.

If I touch the rads, the top is piping hot whilest the bottom is only lukewarm. As I slide my hand up the columns the rads only really get hot towards the top quarter and this is where I'm getting a bit lost as to why....

Every rad bar one upstairs and one downstairs has a TRV fitted. I may have gotten mixed up between flow and return and a few may well have the TRV fitted to the return as opposed to the flow.

I removed all TRV's but this made no difference.

With the TRV's removed I tried to balance the rad that heats up first by all but closing the LS valve and opening by 1/2 turn at a time but still the rad only gets lukewarm at the bottom.

Does anyone have any ideas on what I can try with minimal disruption in oder to dignose why these big rads are not fully heating up ?

Some are bedroom ones are 80 odd cm wide, hall and kitchen ones are 1.2 - 1.5m wide
Bathroom ones are 50cm wide.

The ones with no TRV seem to heat up all over and dont seem to have the same problems as the others. Having said this, with the TRV's removed from the others they are still not getting hot all over....

Many thanks in advance of any replies.

Ron.

 

[lewisplumber]

Is the flow coming in from the top of the rad If so this is where all the hot water is. Heat rises cooler water falls and goes down the return. They are big cast iron rads which use alot of heat heating them up. Could be better moving back to the other stile rads as these will take longer to heat costing you more money. Also when they are hot enough the room stat will stop and shut down. If the one that works is in the room with the stat on the wall and is hot enough it will shut down and the others may not have reached there optimum tempriture

 

[tamz]

It is a flow problem worsened by (but not only because of) having trv's fitted. Have a look in the end of a trv you have removed and you will find out why.

After you have fixed that problem re-balance the full system from scratch.

 

[RonG]

Thanks for both replies.

Regarding the flow - flow is at the bottom of the rad on all rads. Rooms stat is only fitted in the hall about 1.5m away from the hall rad. All but 2 of the other rads have TRV's but no room stats.


I'm alittle confused by the second reply - what should I be looking at with respect to the TRV internals ?

Many thanks in advance.

Ron.

 

[tamz]

A 15mm trv only has an 8mm hole inside which restricts the water flow. Column rads need a good flow of water to heat properly.
You can buy low resistance valves if needed (Danfoss) but first of all check how it has been piped (how many rads are taken from each 15mm pipe).

 

[rdt]

A 15mm trv only has an 8mm hole inside which restricts the water flow. Column rads need a good flow of water to heat properly.
You can buy low resistance valves if needed (Danfoss) but first of all check how it has been piped (how many rads are taken from each 15mm pipe).

I have a similar problem with some cast iron rads. Balancing the system (heavily restricting the flow through the other regular rads) has helped but not fully sorted it.

I currently have Danfoss RAS-C2 TRVs on these rads. What's the Danfoss low resistance valve you mention? Can the sensor from a RAS-C2 work with it, or is an entire replacement TRV needed?

cheers.

 

[Billy Bob Bob]

flow should be on top not bottom and as tamz says trvs are not helping

 

[tamz]

I currently have Danfoss RAS-C2 TRVs on these rads. What's the Danfoss low resistance valve you mention? Can the sensor from a RAS-C2 work with it, or is an entire replacement TRV needed?

cheers.

Danfoss RA-FN valves give higher flow rates through the valve and for larger column rads consideration should be given to RA- G if fitting on 15mm pipe.
The valves come with a 1/2" bsp female thread but internal nuts and rings are available for direct connection of 15 and 22mm pipe.
Both valves can be fitted with the RAS-C2 heads but this will slightly restrict the flow.

 

[WHPES]

Regarding the flow - flow is at the bottom of the rad on all rads.

There's your problem. Flow should come in at the top of your cast iron rads. If it comes in at the bottom, the hot water comes up one stile and straight out of the top, missing out most of the rest of the radiator. Correct this before you spend ages messing about changing TRVs and it should solve your problem.

 

[rdt]

There's your problem. Flow should come in at the top of your cast iron rads. If it comes in at the bottom, the hot water comes up one stile and straight out of the top, missing out most of the rest of the radiator. Correct this before you spend ages messing about changing TRVs and it should solve your problem.

I don't understand that. If flow and return both at the bottom, how could that happen?

 

[Billy Bob Bob]

it cant i suggest you carefully READ all posts again

 

[rdt]

it cant i suggest you carefully READ all posts again

It's a fair cop guv

 

[RonG]

OK, thanks for all the replies so far, I must admit I am a little confused, perhaps I need some clarification before ripping my pipework appart

If the flow coming in at the bottom is the issue, how would changing it to the top make the water flow through all the styles as opposed to just one ? where does the resistance to the other styles come in to play ?

I'm greatful for the advice but would just like to understand this before going any further.

Thanks again.

Ron.

 

[rdt]

My understanding is this:
Both flow and return at the top is an absolute no no. Flow at bottom and return at top (your current set up) is not great.
Flow at top and return at bottom is OK. Both flow and return at bottom is best.

I'm sure someone will correct me if that's wrong.

 

[tamz]

WHPES was thinking you had said the flow was coming in the bottom and the return at the top. They won't work worth a jot like that.

Bottom opposite ends are fine. Top bottom opposite ends work a bit better though (flow at the top, return at the bottom opposite end)

 

[WHPES]

If you have currently set up your cast iron rads with flow at bottom and out at the top, can you switch round the pipework somewhere? (NOT by using flexi connectors that is!!)

The radiator in your photo has a connection at the top which is why I made my post!

The style of cast iron rads in your photo do not work that well with flow and return both at the bottom because of the design of the columns. They are best in at top out at bottom.

 

[RonG]

Hi again,

Thanks for the clarifications. The photo I posted was a picture of the type of rads I have but not the actual ones - it was just for illustrative purposes.

My rads do have one connection top and one connection bottom though, just like the one in the pic. As mentioned, on most flow is at the bottom with return at the top.

Regarding switching them around we have no access to under the floor boards as the original boards are covered with 18mm solid oak. I may have access to one or two rads downstairs via a trap door so may be able to try those. One idea would be to rotate the rads and extend / cut down the piping on each respective side.

With the weather being so cold I cant chance a drain down right now just in case I dont finish by nightfall so may have to wait for milder weather.

Just as a sanity check - to determine flow and return without disconnecting, I take it the hotter side is flow right ?

Thanks again.

Ron.