Central Heating Problem

[duffbrewery]

Hello, I have just turned on my heating for first time in the last week or so after having moved in during the summer.
The hot water is and has been working fine since we moved in but the problem seems to be with heating the rads. Most of the upstairs rads work fine, esp when they have been isolated (ie one turned on at a time) but the downstairs ones seem to vary when they heat up.
The closest rad to the hot water cylinder in the bathroom is the hottest when left on, and the two in the bedroom are reasonably hot when the heating comes on in the morning. The real problem is heating the downstairs and upstairs rads all at the same time. If more than three rads are on at once they are all lukewarm and barely produce enough heat for the room.
The downstairs ones rarely come on and if they do they have large cold spots. If all rads are on, the upstairs ones then start to lose heat. If its any help, I have had at least some heat to each of the rads in the house at some time or another. It seems to be very random.

 

[JohnD]

Have you balanced the radiators?

When you bleed the radiators, what colour is the water?

Does the cylinder get unusually hot when the heating is on?

Do you have a feed and expansion tank in the loft, which keeps the radiator water topped up?

Can you see the circulating pump; what speed is it set to?

read the first few items in here for backround:
//www.diynot.com/forums/viewforum.php?f=7

 

[clf-gas]

As John above and have a read of this here http://www.diydata.com/projects/centralheating/balancing/radiator_balancing.php

 

[duffbrewery]

hello john d

i have tried to balance the radiators after someone at work suggested isolating each one to run the hot water through them. all of the rads upstairs get fairly hot but not as hot as i'd expect. the pipes running from the airing cupboard/to first rad downstairs are piping hot sometimes then seem to mysteriously cool down 15 mins later.

i have done the same with the downstairs ones and the first time i did it they were hot, (but again not as hot as they shouldve been) apart from the large one in the front room which is fairly hot in some parts and freezing in others.

i bled the rads downstairs, and the water was clear-ish (bit murky at first then running clear) on two and dark on the big front room one. haven't bled rads upstairs as there are no drain off valves on any and only old style plugs and as all our carpets are light my missus would go mental if we get black water all over them

cylinder does appear to be very hot as top outlet pipe is baking hot as is hot water from taps. the pump is set to the highest speed at mo but have tried running it at medium speed to. seems to work/sound ok esp as kitchen rad has been baking at times then sometimes lukewarm then sometimes freezing cold

 

[JohnD]

the cylinder gets very hot

this suggests to me that the heat from the boiler is going to the cylinder when it ought to be going to the rads

Have you got an electrically-operated 3-port valve to send the heat to the rads or to the boiler? it might be worn out. it is possible to manually override them but I don't remember how to do it.

There should also be a thermostat strapped to the side of the cylinder. See if you can see what temperature it is set to, and if it clicks "off" when the cylinder is hot. If you can lay your hands on a multimeter you could test it.

If you are getting black water out of the rads then there is corrosion sediment inside them. this can cause partial or complete blockages. The lower part of a rad will be cold if there is a partial blockage but the top may be hot.

Have you been bleeding them from the top or the bottom?

 

[duffbrewery]

sorry didnt mention feed tank. not sure about feed tank. i think boiler feeds rads and hot water tank. i think it is a worcester ultimate which i have heard can overheat and cut out. do you think it may heat the hot water and then cut before it heats the house?? haven't had any hot water probs and have hot water upstairs, downstairs and in shower!

thanks for you help

 

[JohnD]

not sure about feed tank.

go and have a look in the loft then.

If you can post some pics of the tank and pipes in the loft, the pump, valves and pipes round the hot cylinder this could be useful in seeing how your syst is put together.

 

[duffbrewery]

i bled the manky/faulty one in the living room from the top as that was where the plugs were and it only has rad valves with no drain off at bottom (didnt want water everywhere as cant get bucket or basin below)

i thought it might be the 3 port valve (after checking central heating diagram online) but as yet i cant find it. doesnt seem to be near boiler and cant see it in airing cupboard

 

[duffbrewery]

temp on cylinder thermostat seems to be high as previous occupants left it on about 80 degrees

 

[JohnD]

turn it down to 60 or less and see if the HW gets cooler and the rads get warmer.

I hope the cylinder is well-insulated or you are throwing money away in escaping heat

bleedingh rads from the top is correct. Did you get any air out? You ought to bleed the upstairs ones too. Roll the carpet back or cover it if you are worried about spray or drips.

 

[duffbrewery]

i will try that tomorrow. cylinder is pretty well insulated but as you said it is a waste of money just boiling water for taps all the time when i cant heat my rads. is there any easy way to bleed rads from plugs as when i did kitchen, lounge downstairs water sprayed on the walls and floors, but as it was lam flooring and tiles it was easy to mop up. i don't want soak the carpet or floor boards

cheers

 

[JohnD]

I don't know what you mean by plugs. Show us a pic.

most rads have a plug at one end and a bleeder at the other. You can take out the plug and put a bleeder in. If you close the valves at both ends first then (unless the valves leak) not much water will come out

 

[duffbrewery]

nearly all my rads except 2 have old style 3/4" (or close to) iron plugs on both sides that you have to turn with an allen key style spanner.

 

[JohnD]

and have they no brass pin screwed in the middle?

 

[duffbrewery]

no they dont. two have, the others don't