Poor Radiator Circulation

[redcap]

3 year ago had a replacement potterton Kingfisher mf fitted and all my 16 radiators have worked OK up to when I had a replacement I/Direct Water Cylinder fitted.
The previous cylinder had a Thermostatic Valve fitted for the hot water system, but the Corgi engineer employed for the changeover, decided that this TV was not necessary, so it was removed and since completion of this work, all the radiators have struggled to work efficiently.
all the upstairs (6) except the bathroom are permanently turned off and of the other groundfloor rads (10) only 6 seem to heat up and the remaining 4 are constantly cold.
Since these problems started, the system has been drained and re-filled many times with Sentinel X400 sludge remover added about 3 times as is current, the lockshields have been balanced and the whole system was completely power flushed (Aug 2008) @ a cost of £500+, but still we have 2 stone cold and 2 just warm rads, despite the trv's, boiler & room stats all set at maximum, but the tap hot water is scalding and dangerous.

Any suggestions will be gratefully appreciated as none of the 3 different plumbing engineers I have employed seem to have any positive answers.

 

[Gobo]

Is it the two furthest away radiators that aren't heating up? or just two random ones?

 

[kevplumb]

The previous cylinder had a Thermostatic Valve fitted for the hot water system, but the Corgi engineer employed for the changeover, decided that this TV was not necessary, so it was removed and since completion of this work, all the radiators have struggled to work efficiently.

despite the trv's, boiler & room stats all set at maximum, but the tap hot water is scalding and dangerous.

answered your own question

the cylinder is robbing the heating

 

[redcap]

Is it the two furthest away radiators that aren't heating up? or just two random ones?

Yes they are the furthest away from the boiler

 

[Gobo]

I'm not a heating engineer but I was working in a house which had been four cottages knocked into 1 thus had lots of rooms over different levels and some along way from the boiler, they were having a similar problem to you.

It was solved by balancing the radiator valves to be more bias to the furthest radiators, i.e having them completely open and partially closing the nearer radiators. If you have thermostatic radiator valves then this should already be happening. If you haven't thermostatic valves you could test whether this would work by turning off the nearer radiators and seeing if they ones that aren't working come on.

But as Kevplumb said the removal of the thermo valve from the system is the root of the problem.

Gob's

 

[redcap]

I'm not a heating engineer but I was working in a house which had been four cottages knocked into 1 thus had lots of rooms over different levels and some along way from the boiler, they were having a similar problem to you.

It was solved by balancing the radiator valves to be more bias to the furthest radiators, i.e having them completely open and partially closing the nearer radiators. If you have thermostatic radiator valves then this should already be happening. If you haven't thermostatic valves you could test whether this would work by turning off the nearer radiators and seeing if they ones that aren't working come on.

But as Kevplumb said the removal of the thermo valve from the system is the root of the problem.

Gob's

Thanks for that, but all the rads except 2 (in bathrooms) are fitted with TRV's and have been balanced, I have also given tank a clout as Gobo suggested, but still the problem exists although I did sense the furthest radiator was luke warn last evening whereas it has been stone cold for ages so perhaps the X400 sludge chemical is gradually working as it's been in system now about 20 day's.

Are you suggesting that if a thermostatic valve is fitted to the hot water cylinder, this will improve the problem and hot water should reach the furthest rads?

 

[bellairaphon]

have u shut the trvs down except the two that aint getting anyheat and seeing if they get hot?

Nath

 

[redcap]

Not as yet, but I will do so tomorrow and keep you informed about any progress, thanks for that suggestion.

 

[TicklyT]

When the boiler was changed, was your system changed from gravity water heating to pumped water heating?
What controls do you now have for the hot water heating?

Tank thermostat?
3 way diverter valve?
Two zone valves?
Programmer?

You should have some way to control the water heating. A thermostatic valve is just one option. It was common on gravity circulation systems.

For a pumped system, a diverter valve or a pair of zone valves should work in concert with the cylinder thermostat, room thermostat and programmer to control hot water heating times and temperature. The controls should send the entire system flow to the radiators when there is no call for hot water.

A lockshield valve in the cylinder primary circuit can sometimes be used to limit the flow to the cylinder, balanced along with the radiators. Water cylinders for gravity circulation offer less resistance to the primary flow than ones designed for pumped systems.