It's really difficult to say, as different devices act very differently. Some will 'break up' the image, some will black screen, some will tell you there is a signal problem, some will say 'no lock'...it's just impossible to say. Signal indicators rarely mean anything on their own, as you don't really know what value / formula it is using to say the signal is fine.

If you have a high end PC tuner, you can normally examine the transport stream and see what the issue is exactly. These are expensive though and not really a way to troubleshoot.

You can buy a signal meter from ebay for a few quid, but these are normally 'all or nothing' devices, and little drop outs rarely get picked up on them.

It's interesting that you mention it was a few years ago, as this could coincide with the 4G turn on, depending on your area: https://ukfree.tv/maps/4g
4G has caused some issues for TV signals: http://www.techradar.com/news/phone-and-communications/mobile-phones/4g-could-ruin-your-tv-here-s-what-will-save-it-1199804

By far the cheapest way, and least hassle is to renew the equipment. Namely the TV aerial and the coax cable.

The correct coax is really important. If you have older stuff installed, it will have issues with the latest signals. See this for a breakdown and explanation: http://www.satcure.co.uk/tech/cable.htm

Any decent aerial will do. Screwfix and the usual places will have an offer on no doubt.

If you want to 'split' the cable to go to more than one device, you should absolutely invest in a 'mast head' amplifier where your aerial is installed.

Finally, make sure your entire cable run uses F-connectors: http://www.screwfix.com/c/electrical-lighting/lead-connectors/cat830560
EVERY end of the cable should have an F-connector on it, which you can then plug into the correct coupling plug, if one is needed. For example:
On each end of the cable: http://www.screwfix.com/p/f-connector-for-sky-cable-pack-of-10/98173
Need to join 2 together: http://www.screwfix.com/p/labgear-f-plug-to-f-plugs-pack-of-10/95730
Need to use it on a TV with only a 'pin' connector, use these on the end: http://www.screwfix.com/p/labgear-f-to-coax-plugs-pack-of-10/39772
A lot of recent equipment just accepts the F-connector directly. All satellite equipment should by default.

Making a cable is very easy. See: https://www.youtube.com/watch?v=zNqJcmslwyM
You don't need to buy any equipment if you have some pliers around. Although some copper grease is good to put on the cable where the thread will screw onto to make your life easier :innocent:

There are other options, like compression connectors, but you really don't need them for the home.

Hope that helps a bit.

I've been through a number of boosters like this and they were all quite poor. You're boosting an already bad signal, along with the errors and noise in the stream.

You need to put a 'masthead amplifier' close to the aerial and ensure you have good quality coax. High quality coax makes a huge difference alone.

Loads of good reading at: http://www.aerialsandtv.com/loftaerials.html#AmplifiersAndSplitters

wasn't aware something like this existed! brilliant, so does this mean a tv would need a wall socket aerial not an external wirey one?

Thanks OP

With digital TV it's often the quality of the signal that counts not the quantity. If it's rubbish in the first place this may not help.

I've used a similar product before for a digital signal, and they do work. You just have to be realistic about what it can do with what's already a poor signal. I had a few channels that would jump in and out occasionally, and a booster *just* made it tolerable. I went from losing the signal every 10 seconds to slight hiccups every few minutes. People have had success with getting channels they couldn't receive at all before, but I wouldn't count on it working consistently.

I've been through a number of boosters like this and they were all quite poor. You're boosting an already bad signal, along with the errors and noise in the stream.

You need to put a 'masthead amplifier' close to the aerial and ensure you have good quality coax. High quality coax makes a huge difference alone.

Loads of good reading at: http://www.aerialsandtv.com/loftaerials.html#AmplifiersAndSplitters

Lol @ TV ariel. 1999 called they want their technology back.

I don't disagree with what you're saying, but it's highly situational with digital. I've just not had much success myself. Even the devices react differently to poor signals, so it's very hard to make a solid recommendation to anyone (other than a mast head, which will always solve the issue if you can get the signal in the first place). But for 5 quid, it's worth a shot. You can also return easily to Argos if it doesn't work!

On the power front though: Not quite. You can get mastheads you can power through the coax cable. See the link I posted above for an example in one of the images. It means even with no power in the loft, it's trivial to install one :innocent:

I've got a plug in booster from Amazon and it makes the difference between being able to receive HD channels or not in a bedroom. Worth a try.