Boiler Flow Temp Low?

piperm87

Hi all,

I've got a 16 year old Worcester Bosch 28KW greenstar.  I've been going round the house all weekend trying to balance the radiators as i'm not getting heat to the further one in the bathroom and all of them are only getting hot at the tops not bottoms (new radiators). I've got the boiler set to no5 at the minute which is approx 67 Degree's but i'm only getting 50 Degrees a the radiator flow pipes and around 45 - 48 on the returns now i've been around balancing 

I went  and checked the boiler last night as i was confused as to why i'm only getting 50 degree on the flow pipes when its set to 67 degree.. I checked the copper pipe as it exited the bottom of the boiler and i'm only getting 52 there aswell  if this correct as it seems a big difference in temperature from what the set point is to what its actually achieving on the pipes

Many Thanks

Matt

tacpot12

Is it possible that you have weather compensation or load compensating thermostat as part of your system? This might be reducing the flow temperature as it is not that cold outside yet.

If the radiators are new, have the pump speed been changed? I wonder if the hot water isn't getting forced into the bottom of the rads because the pump speed is too low. 

shiraz99

You'll never get the same temp at the pipe than you do as indicated at the boiler, also what are you using to measure the temp, is it accurate enough. Right now, my boiler temp is 60 degrees but the rads are reading around 54. This is more than enough to heat the house. The purpose of reducing the flow temp is to allow condensing to more efficient at the boiler, the only affect it should have on your radiators is perhaps take them longer to reach the desired temp set by your thermostat.

BUFF

tacpot12 said:

Is it possible that you have weather compensation or load compensating thermostat as part of your system? This might be reducing the flow temperature as it is not that cold outside yet.

beaten to it, what controls have you got?

Chickereeeee

tacpot12 said:

If the radiators are new, have the pump speed been changed? I wonder if the hot water isn't getting forced into the bottom of the rads because the pump speed is too low. 

That would be my guess.

piperm87

Hi all

There isn't a weather compensator or anything like that installed on the boiler, Only thing i have is the Hive heating system which consists of the wireless hub and thermostate and 3 Hive TRV's.

How can the pump speed be changed?  We've had this problem since we first moved in, the house was empty for 2 years prior. We've come in and i've been doing the house up ever since. Ive replaced 5 radiators so far and i've removed one entirely but the problem has never gone away, i've tried balancing the system no end too but still have the same problem, even when the flow temp is turned up to full.

piperm87

shiraz99 said:

You'll never get the same temp at the pipe than you do as indicated at the boiler, also what are you using to measure the temp, is it accurate enough. Right now, my boiler temp is 60 degrees but the rads are reading around 54. This is more than enough to heat the house. The purpose of reducing the flow temp is to allow condensing to more efficient at the boiler, the only affect it should have on your radiators is perhaps take them longer to reach the desired temp set by your thermostat.

It just seems more of a drop than i'd be expecting. a 6 degree drop like your getting is to be expected but a 15 - 20 degree drop is a little excessive to me, especially when im testing the pipe as it exits the boiler..    

Oh and i'm using a Tiesto  Water temperature tester that i use at work for monitoring flow temperatures for legionaries.. its fully calibrated and has probes to test fresh water and copper pipes .

Ectophile

Some, but not all, water pumps have a little switch on the side to set the speed. 

Just a thought - is it possible that you've managed to "balance" the system by turning all the radiators' lockshield valves almost off?  If so, then hardly any water would be flowing.

piperm87

Yeah, that appears to be the case. I open the valve in my daughters room earlier which is the closest to the boiler and the whole rad got warm... problem is once i done that it upset the radiator in the bathroom which stopped getting hot.. cant bloody win with the system at the minute ! 

Mutton_Geoff

If you're only dropping 2-5 degrees between flow and return (regardless of boiler temp setting) then you need to reduce the flow rate through the radiators. Ideal temp difference across rads and boiler is 10-12C.

Ectophile

Mutton_Geoff said:

If you're only dropping 2-5 degrees between flow and return (regardless of boiler temp setting) then you need to reduce the flow rate through the radiators. Ideal temp difference across rads and boiler is 10-12C.

Unless all the radiators are off, and the water is flowing through a bypass valve instead.