Bottoms of radiators not getting hot

[joddle]

My system is fed from a Valient combie boiler using 28 mm pipe reducing to 22mm then 18mm or 15mm for each rad depending on their size.
The balancing seems ok as all rads appear to heat at the same time with all rads getting hot - but at the tops only. No matter how long the system runs for the bottoms of the rads remain cool even if the tops are piping hot. Surely this is not very efficient.

The rads are modern aluminium secitonal types variying in size and are connected in TBOE fashion with the hot feed to the top. The installation was done by a local plumber who appears to have a good reputation.

Is this type of connection correct? According to information on the web TBOE seems a bit old fashioned - or should the rads be connected at the bottoms only? - or perhaps fed from the bottoms?

A few thoughts - the system is large - ie the feeds are very long and the house is very ramblng. The main feed starts at waist hight, then goes to ceiling height (3.5 metres) to cross a large room then drops to skirting level for a while then returns to ceiling level to complete the system (total distance 55 metres from boiler to final rad) - a bit odd but the only way to get the pipes from one end of the house to the other and apart from a few early air lock issues which were solved by putting automatic vents at two points, the water appears to circulate fine still being hot at the final rad.

Is the pump in the boiler sufficiently strong for such a system? the boiler seems powerful enough as the heat comes on quickly and maintains temperature in the rooms despite their large size?

Any help much appreciated here....

 

[John506]

You need to flush out your system, the cold parts of the rad is sludge built up.

Look into flushing it out yourself, or if you know how, drain down, take each rad off, take into garden and flush out with a hose pipe.

 

[joddle]

You need to flush out your system, the cold parts of the rad is sludge built up.

Look into flushing it out yourself, or if you know how, drain down, take each rad off, take into garden and flush out with a hose pipe.

Hi and many thanks for that - although I did not say in my earlier post I had flushed out several of the rads but there is no difference on those so far treated in this way - in addition there are two new rads in the system which also fail to warm from the botttom. When the new rads were installed the whole system was flushed thouigh but very little sludge found - however not all the indivudual rads were flushed. The whole system is only a few years old and only used for about 3 months of the year at most - and then only in the evenings.

It appears (although I could be very wrong) that the rads are very efficient and the heat is all dispersed before the water reaches the lower parts - the exit pipes are quite cool compared with the inflow pipe although hotter than the bottom of the rads themselves.

 

[ChrisR]

In that case the flow is too low, either due to a tired pump, undersized pipe, or most likely poor balancing of the system.

Try CLOSING a couple or 4 rads which work well and see if things improve.


----
If you turn the room thermostat up high, does the boiler cycle on and off with the bottoms still cold? If so, the pump isn't doing enough.

TRVs??

 

[advancedplumber]

heating systems are very complex and had to understand. is this oil fired or a gas combi system??? has some plumber came and replaced your old system and redone everything or just put new raditors into the system???? not enough info to help you my friend. top and bottom entry in a radiator system is really dark ages material as folk nowadays does't like pipes showing too much plus top and bottoms is more associated with gravity or one pipe heating systems, again really old stuff. this is 2008

 

[joddle]

heating systems are very complex and had to understand. is this oil fired or a gas combi system??? has some plumber came and replaced your old system and redone everything or just put new raditors into the system???? not enough info to help you my friend. top and bottom entry in a radiator system is really dark ages material as folk nowadays does't like pipes showing too much plus top and bottoms is more associated with gravity or one pipe heating systems, again really old stuff. this is 2008

Many thanks to last two contributions - dark ages it may seem but here in Spain ALL systems are seemingly done this way - as for cycling the answer is yes - even with the boiler stat turned up full - the rads tops get very hot but bottoms still remain cool but the boiler does fire up and shut down so maybe it is a pump problem - tried having the room stat up as well - however we had the boilder serviced a few days ago and the engineer said the pump was fine!

 

[JPC]

tried closing some working rads down to see if this cures the none working ones as chris mentioned

 

[advancedplumber]

just another thought. i have been getting alot of radiators from the continient which are top and bottom entry connections. these are not standard myson types and are baffled, meening the water can only travel through one direction. i came upon this problem and the rads wouldn't heat . the manufacture can tell you what side to take the flow in on. the flow side is easy to tell as its the warmer pipe of the two sides. this can sometimes be over looked.

 

[joddle]

Well - thanks for all the replies and I have been trying out the things suggested with some success. With just over half the system closed down the other rads then do warm up better but I decided to look at the potential lack of flow and noticed something which may or may not be contiibuting to the problem.

On opening the boiler I see that the CH connections have been restricted - ie there is a section of 15mm pipework in both the main feed and the return - on the flow this is only in the form of a 15mm elbow close to where it finally joins to the boiler outlet. The pipe then widens out again to the full bore size - ie the same size as the pipes inside the boiler. The other CH pipe has a section of smaller bore pipe between the boiler junction and the main feed pipe again seemingly restricting the flow - could the narrowing of thes epipes be the cause of my problems - and could they also be responsible for the rather high noise level I have always had from the system.???

 

[daveaf]

Having a restriction so close to the exchanger will certainly cause you problems, it would have the same effect as a clogged exchanger restricting the flow. The noise you have on the system is probably also due to these restrictive elbows, They are preventing adequate flow through the boiler and so the water will be boiling in the exchanger, this will only get worst as the boiling starts to build up lime scale.

Remove the 15mm elbows and replace withh 22mm