Central Heating problems

Mr_Tilly

My first post as I am at a loss to understand what's causing a problem we have with our heating.

Could anyone give me some advice about what is causing the problem please and how I could potentially fix it? The house is uncomfortably cold and there's another cold snap on the way.

Problem:

Temperatures of radiators inconsistent - some cold, some lukewarm, a couple normal.
Problem is worse downstairs.
House has a ground floor and 1st floor.
Some radiators feel colder at the bottom


Actions taken:
Bled radiators

Bled a vent valve on the magnetic filter, next to hot water cylinder

Checked expansion tank is full in loft

Turned off the lock valve and thermostat on unused radiators (obviously we expect these to be cold) - in an attempt to provide hot water only to the required radiators.

Central heating boiler set to constant and 70 degrees

Thermostat on the hot water cylinder changed from 60 degrees to 80 degrees

Plenty of very hot water in the taps but still radiators feel mildly warm.

Thermostat in hall now set to 25 degrees, but using a thermometer, actual temperature is 16 degrees.


My understanding:

Hall thermostat is creating the demand for heat
The gas boiler is responding because its on and heating water
The thermostat on the hot water tank is set high to provide hot water to the radiators
The pump is working on its maximum setting to push water around the system
The three port diverter valve has been set to manual to force water to the central heating system


Any help very much appreciated.

Mr Tilly

Mark_Mark

Are you sure the pump is working?

Mr_Tilly

Mark_Mark wrote: »

Are you sure the pump is working?

Hi Mark, if I change the dial from High speed, to Low speed to off, I can feel and hear it doing less or more, depending.

I've just turned all thermostats and all lock shields off, except for one downstairs radiator, to prove whether the hot water pumps to the downstairs.

Mr Tilly

TeamPlum

My suggestion is to turn the thermostat up pretty much as high as it will go. This keep the water/air moving in the radiators (and you need the air to be moving for a while). The trouble with trying to do this at a lower temperature, is that the water soon reaches temp and the pump shuts off, trapping the air in the current radiator.

Because the air/water mixture is moving, the air can get to the highest radiator in the house, which you can then bleed. (Then go on a bleeding rampage of the lower rads)

Hope this works for you, takes some time for the air to reach the highest point. This worked for mine, I can only hope it worked for yours.

In addition, how old is this system?

Slowly_does_it..

Rads that are colder at the bottom have sludge, colder at the top have air in the system.

You say you have bled the magnetic filter, have you cleaned the filter itself? They vary by make on how this is done.

When you do this what colour is the water? - if really bad, a full flush would be needed, if not too bad you might get away with replacing a lot of the water in the system, and probably doing a chemical flush as well. Remember to open all the rads up again while flushing the system!

Mr_Tilly

TeamPlum wrote: »

My suggestion is to turn the thermostat up pretty much as high as it will go. This keep the water/air moving in the radiators (and you need the air to be moving for a while). The trouble with trying to do this at a lower temperature, is that the water soon reaches temp and the pump shuts off, trapping the air in the current radiator.

Because the air/water mixture is moving, the air can get to the highest radiator in the house, which you can then bleed. (Then go on a bleeding rampage of the lower rads)

Hope this works for you, takes some time for the air to reach the highest point. This worked for mine, I can only hope it worked for yours.

In addition, how old is this system?

Thanks Teamplum - I've had the boiler stat cranked up to 80c all afternoon but only for the central heating. The settings for hot water have been disabled. I've opened up all lock shield valves and thermostats on all rads. The bleed on the magnetic filter has released a bit more air as a result, the water is clear after the air release. System is 14 years old but the gas boiler is about 7.

Slowly_does_it.. wrote: »

Rads that are colder at the bottom have sludge, colder at the top have air in the system.

You say you have bled the magnetic filter, have you cleaned the filter itself? They vary by make on how this is done.

When you do this what colour is the water? - if really bad, a full flush would be needed, if not too bad you might get away with replacing a lot of the water in the system, and probably doing a chemical flush as well. Remember to open all the rads up again while flushing the system!

Slowly - I agree on the sludge comment but I was once told that micro bore doesn't get sludge. I have cleaned the filter several times, the magnet is covered in black 'sludge' which I wipe and wash off.

Mr_Tilly

Update - I'm suspicious of the three port distribution valve...

So, with the hot water (taps) demand disabled at boiler controls, I turned down the thermostat on the side of the hot water cylinder. I left the boiler at 80c for the central heating and after several hours felt the A-side pipes from the valve to the hot water cylinder and it was roasting hot. The B-side pipe for the central heating was also hot. I think it's broken and is permanently supplying both no matter what the demand.

Make sense?

Mark_Mark

Mr_Tilly wrote: »

Thanks Teamplum - I've had the boiler stat cranked up to 80c all afternoon but only for the central heating. The settings for hot water have been disabled. I've opened up all lock shield valves and thermostats on all rads. The bleed on the magnetic filter has released a bit more air as a result, the water is clear after the air release. System is 14 years old but the gas boiler is about 7.




Slowly - I agree on the sludge comment but I was once told that micro bore doesn't get sludge. I have cleaned the filter several times, the magnet is covered in black 'sludge' which I wipe and wash off.

I think the sludge comes from a chemical reaction inside the radiators so has nothing to do with the size of the pipes. Once formed microbore is more likely to block due to the smaller diameter of the pipe.

Mr_Tilly

Mark_Mark wrote: »

I think the sludge comes from a chemical reaction inside the radiators so has nothing to do with the size of the pipes. Once formed microbore is more likely to block due to the smaller diameter of the pipe.

That's what I thought...smaller bore quicker to block than larger. Do you know if putting chemicals in the expansion tank is the way to unblock or does each effected rad have to be removed and flushed through?

Mark_Mark

Mr_Tilly wrote: »

That's what I thought...smaller bore quicker to block than larger. Do you know if putting chemicals in the expansion tank is the way to unblock or does each effected rad have to be removed and flushed through?

Depends on how bad it is, you may need a power flush.

southcoastrgi

of course both sides of the mid pos valve are hot because you have put it in man which opens up both sides, turn your cylinder stat back down to 60d this controls your hot water temp coming out of the taps it has nothing to do with your rad temp

it could be a faulty mid pos valve or pump but most likely the system is full of sludge & needs cleaning out, which can be a right pain in the backside on microbore even for a plumber with a powerflush machine