Low lvl LK instances seem difficult to heal

[Fichek]

Like lots of people have already said - go holy. Much easier as holy. You can get the job done as disc but if you want it easier, go holy.

[draticus]

Try out Holy. I find it to be much stronger, especially in 5mans and pre-80.

I have to completely disagree. The first time I changed to disc while queueing as a healer between 70-80 I remember being blown away by how easy disc was, mostly due to mana usage. I use in order from most often to least often: Shield + PoM + Penance + renew + Flash heal + Prayer of healing

[Isvan]

the Rune of Flame (ie the hardest hitting AoE effect which is probaly what causes you trouble) can be dispelled from the mobs like any other magic effect. If it's throughput and not mana which is the problem, just bash out a mass dispel over the mobs. Makes most of the instance far simpler.

[Ultima]

I levelled as Holy when Wrath was first released. I hate healing heroic dungeons as Holy as the throughput sucks, I find it much easier to heal as Discipline in dungeons. I don't think PW:Shield is effected by Mortal Strike, after all.

So, you said the spells that you use. (You forgot to mention Prayer of Mending, which I like to call "Prayer of Win". Spam it on the tank.) However, you didn't say how you heal? Are you one of those players who will cast a spell and then wait 5 seconds to cast another? Or do you spam Flash Heal? I'd say to not bother with Renew if the tank is taking constant heavy damage.

And yes, sometimes the tank is just in bad gear. It can't be helped, there are Death Knights that enter Utgarde Keep in their level 58 Blue Gear, "because it looks cool". You will find Bears who don't spec into Survival of the Fittest, "because it only gives 6% stats wtf". You will find Paladins who use two-handed weapons and Warriors don't know what a CD or Spell Reflect is.

TL;DR - Spam your Flash Heal. Use Prayer of Mending. Don't worry about your mana pool during the trash pull, make it clear you need mana breaks in-between though. Use your Shadowfiend for mana. And most importantly, very very importantly. If you have dual-spec, check your spell ranks on both of the specs you have. Spell ranks do not get updated in the spec you are not currently in. This happens all the time, I once had a Paladin apply to a guild who used low rank heals in Icecrown. He had been 80 for a very, very long time.

[Sarcasm]

I see nothing wrong with the spec. Which spells are you relying on? Try to stick with PW:Shield, Penance, PoM and Flash Heal. I would suggest dropping the Penance glyph for the Flash Heal glyph if you are having mana issues.