Back Boiler to Combi - should we replace the pipes?

Holly_BC34

We've just bought a new house which is heated (and hot water which is working fine) by a back boiler. We got the keys last week and nearly all of the top floor radiators worked (3/4 - not the main bedroom) but the bottom floor radiators didn't work at all - pipes leading to them however were hot. We've now lost all heat to all radiators and none of the pipes are working but we still have hot water.

Money is TIGHT but we found a pay monthly deal with a company called BOXT who can replace the radiators (7) and boiler (about 5k) but cant upgrade the pipes - should we do this now as they've said the pipes might burst due to them being too small.

Bendy_House

Well, pipes certainly won't burst because they are too small. That was a strange thing to say - I wonder what they meant by this?

They might develop pinholes for other reasons, such as poor quality copper coupled with a soft - acidic - water supply. And they might expose weak points/joints due to the new boiler almost certainly being sealed and pressurised - ie running at 1bar and above, whereas I'm guessing your existing system is vented, with a wee F&E tank in t'loft (so running at ~0.1bar).

Can you tell us what size your existing pipes are?

It is reasonably common for radiators to develop leaks when a system is upgraded to 'unvented' (pressurised), but this will only be if they already have significant internal rust, and are thin-walled as a result. The fact that some rads aren't even heating up does kind of suggest that there is a large amount of sludge in your system, sludge being caused by this internal corrosion.

It's impossible to judge what the true situation is like from this side of the screen, but perhaps a useful pointer would be to remove a rad from the downstairs circuit, take it outside, and see what you get when you hose it through whilst thumping it with summat soft/hard. Check along the bottom of the rad - any signs of bubbling paint? Any indication of leaks?

To try and answer your Q - provided the existing pipes are (a) of adequate size to supply the rads - and surely they are - and (b) plumbed in an adequate way - ie 2-pipe system - then I personally wouldn't have any concerns about reusing them; copper tends to last for a looong time. But I would have the whole system thoroughly power-flushed.

The rads would need checking to see they are ok. You'd likely want new TRVs fitted - perhaps even 'Smart' ones on the most used rads - and if you replace any rad, then seriously consider going 'over-sized'. Ie, choose one with a larger output - say going 2-panel from one, or double-finned from single, that sort of stuff - because this will mean it'll give the same heat output as before, but with a lower water temp = more efficient.

nofoollikeold

1. Pipes don't burst because they are too small.  What can happen is if you change from a conventional boiler to a combi boiler, the greater pressure in the pipes can cause leaks.  However these are usually at joins in the pipework or where pipes connect to e.g. radiators.  
2. If your hot water is OK, then if your hot water is heated by the boiler, the boiler is working and the fault is likely to lie elsewhere, for example in a motorised valve.  Changing a valve is much cheaper than changing a boiler!
3. If you let us know the following better advice can be provided:
3a. Make and model of boiler.
3b. Whether you have a cold water storage cistern (large) and / or a smaller cold water tank, probably in the loft.
3c. How your hot water is heated.  Photographs of the airing cupboard showing the hot water cylinder and any valves would be useful.
3d. What controls you have in terms of room heating thermostat(s)m hot water cylinder thermostat and programmer.

Holly_BC34

Thanks so much for the advice guys. 

So I think the pipes are 6mm and It's a baxi bermuda ...xi

So next steps I'm going to:

Get someone out to service the current boiler
Check radiators for sludge

Fingers crossed its something we can bodge for now and then save to replace the whole thing when it actually dies.

Bendy_House

6mm is around the thickness of a pencil, and none of these pipes are that thin.

It's difficult to see what size the pipes are - there's clearly some 22mm and 15mm pipes, as you'd expect, but how they are arranged can't be seen. Ie, you'd expect the main flow from the boiler towards the rads would be in 22mm, but this would soon 'tee' off in 15mm to each rad or pair of rads.

We also cannot see where the pump, is, or whether you have any motorised valves to control the boiler's supply to the rads and/or the hot cylinder. There's even a chance it's so old that the hot water heating is gravity, and only the rads are pumped.

You've shown a room stat, but what makes the hot water and/or rads actually come on? Where is the 'timer'?

A good, trusted, recommended GasSafe is your best bet - they will assess what you have, give their opinion on whether it can be nursed along for a while, whether you have sludge, and give you options to either replace or maintain.

Do you know folk locally who can recommend a plumber for this?

Let us know how you get on :-)

Bendy_House

It'll also be worth starting to consider what type of boiler to replace it with, should it come to this. If you have a good water mains flow and pressure, then you can consider getting rid of these tanks in the roof and going 'unvented'. Or even losing the hot storage cylinder as well, and going 'combi'. There are pros and cons.

Section62

Bendy_House said:

Do you know folk locally who can recommend a plumber for this?

Ideally someone independent, and probably approaching retirement... I.e. who will know how this kind of system works and has the skills to sort it out, rather than just wanting to 'sell' the most expensive replacement option.

FreeBear

Baxi Bermuda - No fancy electronics to go wrong. About the only thing likely to fail is the thermocouple or gas valve. The former is around £10, the latter £70 (plus fitting). Whilst not the most efficient of boilers, they rarely go wrong - There are a few things you can do to improve efficiency slightly..

The fact you have hot water shows that the boiler is firing up, so no heat from the radiators is either a faulty timer (but that usually stops the hot water as well), or a failed pump. If you can find the pump, put your ear close to it and see if you can hear it running. If the pump is working, you can quite often hear the water circulating through the radiators.

Things to do to improve the efficiency -

• Fit TRVs to all the radiators except the one closest to the thermostat.
• Bleed & balance the radiators.
• Fit a more modern timer.
• Replace the current thermostat with a programmable one that allows you to set different temperatures during the day (Drayton Wiser is a good one).
• Put an insulating jacket over the hot water tank - Even although it is insulated, a jacket will cut heat loss a bit more.

No need to go rushing out to replace the boiler just yet - I still have my old Baxi chugging away.

Bendy_House

FB, is yours - and could Holly's - be gravity hot water? Or do you have a 2 or 3-way motorised valve?

Holly_BC34

Yes we do have gravity hot water so I'm guessing it's the pump - I'm going to try and get someone out asap to have a look as if its that I'll be saving a whole heap of money and stress. 

If I take the radiator off to do a sludge check do I just need to turn off the water - is it an easy job or should i ask the plumber/gas guy to have a look.

Thanks so much for all the help so far!!!!!!!!!!!!!!!

Bendy_House

Yes, it could be a partially-blocked pump, or one that's underperforming, but there could also be more going on, like sludged-up pipes. Locate the pump, listen to it - does it hum/whooosh quietly or does it sound rough? Check the speed setting - it'll likely have 3 - what's it on?

A quick simple test to see what's causing the cold rads downstairs is to close off every rad upstairs - the ones currently 'working' - and then see if the downstairs ones heat up at all. If they still don't, then I fear a blocked pipe on the downstairs run.

You can DIY a lot of these, and further, tests, at least to hopefully find out what's going on.

Please report back on the above first.

Ok, assuming the downstairs rads still don't heat up... Turn on the upstairs ones again to get back to where you were before. Then select a downstairs rad, the one closest to the boiler, and that isn't currently working at all. Take a photo of it, please, so we can see the valves.

A bit about valves: Each rad has two valves; one of these is a 'control' valve which has a 'head' or knob which is easy to turn? Cool - that's how you turn it up and down. This might be a TRV head, in which case it should be able to automatically control the temp in that room to some degree.

The other valve is a 'lockshield', and is NOT designed to be twiddled with. They usually have smooth caps on them that you need to remove/pull off - perhaps held by a central screw - to allow access to the spindle below which is used to 'balance' the radiator.

'Balancing' means that each rad in a house is set to receive roughly the same amount of 'flow' from the boiler as every other one. Obviously some rads are bigger than others, and some further away - balancing them via their respective L/Ss lets them get roughly the 'same' amount of hot water, so they all heat up at the same time with the right amount of supply.

Ok, L/Ss should always be returned to the setting they were at before you started the job so's the rads are still 'balanced' when you've done. Therefore, you need to note down what each one is currently set to; pull off the cap, and put a pen mark on the side of the spindle, or tape a wee paper flag to it. Now close it off fully - turn it clockwise - until it stops. Count the turns and part-turns it took, and write that down for each one. You'll likely find it was not a lot - a couple of turns-ish.

Ok, in order to check the condition of your system, it may be worth removing a rad - the one mentioned before, downstairs, closest to boiler, and not currently working. Close off both valves (noting the LS position). Place a shallow container under one valve (and have towels etc handy...) and undo the nut between the valve and the rad. Follow? If not, post a pic of it and we'll tell you. Obviously the water in the rad will start to come out, and this could be black and messy - so be prepared. You'll need a shallowish dish to slip under the joint, and a larger container to repeatedly empty this into. A good tip is to NOT undo the connection FULLY, but almost so - leave a thread or two still binding so you can control the flow, and even do it back up quickly if you panic! Make sure the joint is loose, tho', and water will start to come out in a trickle. Open the rad's bleed screw - and water should come out the joint more quickly, but you should have good control over it - you can close the bleed screw to slow it down, or do up the actual joint to stop it fully.

Don't panic - you'll find you have full control over this - bleed screw, and actual joint. Ok, let it drain fully until no more water comes out - the rad is now almost empty, but will likely have dirty water in the bottom. Do up the bleed screw, fully undo both valve connections to the rad, and gently prise the valves away from the rad so the rad can be removed. S*** will come out - have sheets/towels!

Lift the rad straight upwards to disengage it from the brackets, pull it forward away from the wall, and turn it upside-down in order to keep the mess now in the top.

The rest of your system can carry on running without this rad.

Take it outside and hose it through, whilst giving the bottom area some gentle (wrapped in cloth) clumps with a mallet or similar. Basically see what comes out - that'll tell you a lot about your system.

Ok, back inside - shut off the boiler and pump. Fit a container in front of an open valve end, and open the valve - water should come out with a decent flow. Does it? Any carp? Close that valve. Repeat at the other end.

Please report back.