2 boilers can make a good economic (purchase price) case, but I doubt you really need more than about 100 - 120kBtu, so it's not really big enough. All decent boilers modulate down to 25% output, or thereabouts.
Get rad specs from p[lumbers merchants, or online from Myson, Stelrad, Barlo. If yours don't have convector fins, take 25% off the output of a similar sized one which has.
Sounds like your boiler is furred up, sooted up , or something fairly drastic!. Check your rads for sludge (search forum) - and if necessary get it powerflushed.
If you have a couple of showers to run at a time I'd recommend an unvented hot water cylinder if your mains supply is good enough (would need testing), and maybe a Keston condensing boiler, or maybe a Bosch Greenstar, though they have aluminium heat exchangers, which worry many of us for long life.
Also look at your rads - new ones aren't all that expensive if your old ones are sludgy or beaten up. There are heat loss programs on line - Myson and Barlo again. Those sums are the starting point to a warm house.
Remember to allow a fair bit on the boiler size for heating up the HW cylinder if you have 4 or 5 kids! The coild in them these days are very quick - around 25 kWatts.
If your mains is poorish you'll have to keep to a gravity system for HW, possibly pumping showers.
Get rad specs from p[lumbers merchants, or online from Myson, Stelrad, Barlo. If yours don't have convector fins, take 25% off the output of a similar sized one which has.
Sounds like your boiler is furred up, sooted up , or something fairly drastic!. Check your rads for sludge (search forum) - and if necessary get it powerflushed.
If you have a couple of showers to run at a time I'd recommend an unvented hot water cylinder if your mains supply is good enough (would need testing), and maybe a Keston condensing boiler, or maybe a Bosch Greenstar, though they have aluminium heat exchangers, which worry many of us for long life.
Also look at your rads - new ones aren't all that expensive if your old ones are sludgy or beaten up. There are heat loss programs on line - Myson and Barlo again. Those sums are the starting point to a warm house.
Remember to allow a fair bit on the boiler size for heating up the HW cylinder if you have 4 or 5 kids! The coild in them these days are very quick - around 25 kWatts.
If your mains is poorish you'll have to keep to a gravity system for HW, possibly pumping showers.