When a house is built the plumbers rarely come back to the finished house and 'balance' the system, so most, if not all, houses have 'hot rooms' and 'cold rooms'. However, that's not how it's meant to work, and it's easily fixed.
Turn the house thermostat (usually in the hall) to a level representing 'kill me with heat'.
Turn the gas boiler thermostat (on the boiler) down to nearly-off, it clicks when it's fully off. This will set the boiler to it's minimum output, but remember that the water (both warm tap water, and radiator water) may cycle through the boiler multiple times before the tap water or house is 'warm enough'.
Set the heating pump to it's slowest setting - it usually has low/medium/high settings, and determines how fast the radiator water cycles around the house. The faster it flows, the faster the 'furthest' radiator from the boiler heats up, but the more knocks, 'water hammering' (a sound like someone hit a pipe with a hammer, typically when the pump starts) and air bubbles (due to 'cavitation') you get in the sytem, all not good things. The air bubbles get caught in the tops of the radiators, making the radiators considerably less efficient, see below on how to detect and remove trapped air from radiators.
Turn on the heating, and let all the radiotors warm up.
Check the temperature of the top and the bottom of each radiator. the top should be hotter than the bottom (warm water rises to the top of the radiator). If it's cooler there is air in top of the radiator, which can be removed by turning the bleed screw at the back or end of the radiator - you should hear a shhhhhh as th air comes out, when all the air is out, water comes out. If the bottom of the radiator isn't warming up at all, or if the top/bottom difference is very different to other similar-sized radiators, their may be sludge(rust) in the bottom of that radiator, which can only be cleared by removal/flush of the radiator, or (harder) through flushing the entire system.
Once all the radiators are 'bled' of any air, check top, bottom, left and right of every radiator. Top/Bottom confirms their is no air. Left/right tells you which end is nearest the boiler, and is called the the incoming valve, this is normally NOT the one 'used every day' - but it may be for poorly fitted systems.
All the incoming and outgoing valves should now be set to fully open/on.
Go around the house and record the temperature of the left/right of each radiator.
The radiator closest to the output of the boiler will be very hot, the one furthest, and nearest the boiler 'input', will be the coldest. Radiator order rarely makes much sense, as the shortest pipe pathway is the cheapest for the plumber who installed the system.
The 'end' or coolest radiator can be used as a 'sink' for excessive heat in the pipe, before it goes back into the boiler. Just leave both it's valves permanently fully open. As the boiler uses roughly the same amount of gas to heat 10degC water up to 60degC as it does 30C water up to 70degC, using this 'sink' radiator can mean the house heats up quicker, and the system shuts off sooner.
Now you have temperature readings for in/out each radiator, you can see roughly what the midrange *maximum* temperature you should be aiming for. Some radiators, e.g. larger rooms, or those that are on the cold side of the house, or those with large windows, or those where the doors are always open, you may want 5-10degC hotter, smaller rooms, or ones with small windows, you may want to make 5degC cooler. (these smaller rooms tend to have smaller radiators anyway, so 5degC less is probably enough).
Now starting with the hottest radiator, limit the input (hot side) valve - say if 7 turns is fully-on to fully-off, close it by 2 turns, continue this for all the 'hottest' 50% of radiators. The hot water now bypassing these radiators will go into the cooler radiators in the chain, balancing them all to similar temperatures. Aiming for them all to be within 15decC is about reasonable.
Don't worry if they are all now too hot, this is only adjusting the maximum temperature, once all the radiators are balanced, as per normal daily routine, the output (cooler side) value can adjusted provide the 'right' heat output for the weather - however once the radiators are balanced, altering these will be much less frequent that usual, as no single room will be significantly different (and therefore needing 'local adjustment') to the other rooms.
Repeat going around the house, recording the left/right temperatures and adjusting until you're comfortable that no radiator is too cold at the expense of another being too hot. Always remember the order of the radiators, and that altering one 'upstream' will affect the temperature of all those 'downstream'.
Once finished replace any value-caps on the input/hot valves, and return the tap-knobs to the output/cold valves, so that it's clear which side should be adjusted for daily requirements.
The whole house should now warm up together, without particular rooms being really hot or or really cold.
If the 'furthest' radiator take significantly longer for the radiators to warm up, try increasing the speed of the pump one setting.
If all the radiators just aren't warm enough, increase the thermostat on the boiler, and re-check the radiator balancing.
If one radiator is unnecessarily a little (5degC) warmer and cooler than the others, carefully reduce the input to the radiators closer to the boiler ('upstream'), until they are all balanced again.
Enjoy a correctly working heating system, using less gas, less electricity (remember, the pump really eat electricity), but yet warming all the rooms up together, and quickly!
Extra things to do.....
The water in the heating 'header tank' (usually in the attic, next to the cold water store) should contain enough inhibitor that a jam-jar of it won't rust a normal iron nail even after two weeks. Radiators are made of steel, so inhibitor prevents them rusting internally, keeping the system running effeciently, and prevents rust clogging up the radiators, and radiator taps. It's absolutely not something to skimp on !
The water pump can capture an air pocket (especially if it is/was set too fast), which prevents it being efficient, and makes it work harder to do the same job. At worst, these air pockets can result in early demise of the pump. They typically have a bleed screw to let out this air, so for thoroughness, it's worth bleeding after you've messed with the system, it just to be sure. The water pump uses a significant amount of electricity when it's running, so making it efficient - and using the slowest speed setting directly saves you money.
Don't forget to re-adjust your electronic timer - you'll probably need the system on for much shorter times, starting later as it will warm up quicker.
Be aware of the placement of the whole-house thermostat (usually in the hallway), as this determines if the system comes on, if the whole house seems to get too hot, it may be that the hallway radiator isn't hot enough. You really shouldn't mess with the 'daily adjustment' tap of the radiator in the room with the thermostat, as that will obviously affect the whole house in odd ways.