Too many rads for my boiler ?

PrivateRyan

I have an old Glowworm Space Saver 38 boiler (i've read this is 40,000 btu ??). My house has 4 (perhaps 5) more radiators in it than it had originally (now 11 rads). I am struggling like mad to get 2-3 of the rads to temp. I'm a complete (complete !) novice. I've used the lockshields on the rads that are getting hot - it helps a bit, but the last 2-3 rads are 'just' above room temp at best. So, my question is - do i need a new boiler ? To be fair, the old 'git' is heating the water very quickly/hotly and most of the rads are boiling hot ... it's just the last couple.
I've had the water drained/flushed. Didn't do anything. Perhaps the pump isn't strong enough ?

Ideas ???

DVardysShadow

So you have opened the lockshields on the cold rads. Good. Now you must try closing the lock shields on the rads which are hot. Ideally close them completely, apart from the ones you have already opened. Now, open them slightly, until the rads begin to warm. Once you have reopened them, check for new cold rads an d open these lockshields some more,

If after thsi and running the system for several hours, if your boiler remains on constantly for more than 20 mins, you can assume it is not man enough for the job, But if it switches off for a few minutes in the time, it is probably OK

Wookey

With 11 rads and heating hot water you are looking at a boiler with an output of up to 90k btu, size up the rads you have and allow 8000 or so for the hot water tank, the total you come to is what your boilers output should be and leave a bit of headroom.

SOSAGES

11 rads in my house and the output is roughly 40k btu
upstairs are singles (as i expect is the case in most houses)
boiler can do 60k btu max - i figured hot water would be around 10k ..

PrivateRyan

Thanks for all the responses! I've closed the lockshields on the rads that were getting nice and hot - and turned them 1/4-1/2 open, and the rads are getting quite warm (not boiling like before - but very acceptable). The rads that weren't getting hot have their lockshields fully open, they are getting a little warmer but still just above room temp.

If i close all the lockshields and open on only one rad - i can usually get that rad to get hot (although one rad simply refuses and at best just gets about room temp). But by the time i've opened up a couple of others (only a fraction) the rads go cold again.

The boiler is on full - and i'm fairly sure it does switch off for a few mins (which worried me at first - but it sounds like you are saying this is ok?). The water is always piping hot and my pal checked something in the airing cupboard and confirms that it's set to central heating for the priority (there's some sort of tap that can put more emphasis on hot water as opposed to heating ???) [remember - i'm a complete novice folks !]

Could it be my pump isn't strong enough to pump the water around the house ? Right now (today) i have 3 of the rads lockshielded off and 3 of the rads with the lockshield open just a nats ... and still i've got 2 rads just above room temp and one that is sincerely cold.

Any more thoughts ? Thanks in advance.

keystone

OK this may sound a bit off the wall in the context of this thread but so far noone has mention the valves on the flow side of the circuit and thats really what matters. The LSVs aren't there to control whether the rad comes on or not they are there to regulate the flow such that an approximate 11 degrees C temperature drop is achieved across each rad when each one is on. Its called a balanced system and in reality thats what you are starting to move towards based on previous posters advice. So we need to look at the flow side of things.

Do all your rads have thermostatic valves on them? If so remove the heads from the three which don't heat up and make sure that the spring loaded pin on to of the valve itself operates correctly by pushing it down and letting it come backup again.

With the heads off do these rads now heat up?

Have you tried to increase the pump speed and see what happens - no not now - one thing at a time. TRVs first.

Cheers

Wookey

The vast majority of pumps are bog standard, it wouldn't be cost effective to manufacture smaller pumps for smaller domestic installations, check that the pump valves are fully turned on and that there is no air trapped inside it. If all is well then its just simply that there is not enough heat being generated to supply all the rads with hot water, that means that the heating power of the boiler is not high enough to heat the volume of water being pumped thru it.

Switching the hot water tank to priority and then heat the rads next may help very slightly, idea being that once the stat shuts the hot water tank of then all available heating is pushed round your rads, any gain will be minimal though.

greyteam1959

Most central heating pumps have 1 2 or 3 speed settings...if it is on number 1 try turning it to number 2

Wookey

SOSAGES wrote: »

11 rads in my house and the output is roughly 40k btu
upstairs are singles (as i expect is the case in most houses)
boiler can do 60k btu max - i figured hot water would be around 10k ..

Without taking into all considerations of house type/age, heat loss, insulation, rad sizes/type and age its impossible to gauge one house with another, even two that are in the same street can vary greatly. More modern houses will be of a far better build quality, they will also tend to have slightly smaller rads (small bathroom, en suite, small utility room etc) 3 rads that are in those room types will essentially have same kw rating as 1 large rad.

keystone

Wookey wrote: »

The vast majority of pumps are bog standard, it wouldn't be cost effective to manufacture smaller pumps for smaller domestic installations,

That would be why Grundfos make 15/50 and 15/60 versions of their circulators then. The 15/50 is for smaller instalations.

Cheers

Wookey

keystone wrote: »

That would be why Grundfos make 15/50 and 15/60 versions of their circulators then. The 15/50 is for smaller instalations.

Cheers

Yip but then i and probably 99% of other plumbers aren't going to use the higher head pump in a normal domestic situation, perhaps with 14-15+ rads or a 3 story house you would look to the bigger pump but the smaller pump will work for probably about 90% of UK households, with my earlier post i was implying that manufacturing smaller pumps for pumping a few rads wouldn't be worth the trouble, the OP's house did start of with 6 rads.