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?