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Discuss After new rad fitted boiler doesn't want to switch on in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

diy_massacre

Messages
38
Hi

Could you give me some advice based on the following points below?

System background (small cottage) it has
----------------------------------------------
  • System Gas boiler ground floor Greenstar Ri think its a 15;
  • Two gravity fed header tanks in the loft one small one for the radiators and the other much larger for cold water
  • 3 rads downstairs and 4 rads upstairs, 3 beds and bathroom.
  • Indirect hot water hot tank on first floor.
  • Everything is pretty normal in my book except the rads are run off 8mm tubing which I have never seen before and most rads are run from the loft. system boiler has 22 mm pipes which they transpose to a 22mm to multi-output 8mm type distribution pipes,

What actions I took to change
----------------------------------
  • Its all worked well until I drained the system today, closed the stopcock to the small tank in the loft.
  • Fitted a new radiator in the master bedroom. Really I swapped the old one for a new one and repiped the new one to the older pipes. This was to put the bed up against the wall.
  • After fitting the new radiator I opened the stopcock to the small header tank and bled all the radiators and opened all the values. I also bled the cock above the boiler in case I any air came out. There was appropriate gurgling when bleeding the rads.

Outcome / Problem
--------------------------
  • The boiler comes on but and starts making starting sounds but then closes down. The output pipe of the system boiler is hot so it's working correctly.
  • Hot water or heating doesn't work.


Please can you advise what you think it wrong, I dont believe I am able to bleed any more radiations, have looked at numerous posts but they have not resolved the issue.

Kind Regards

Matt
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
Messages
29,465
Solutions
1
Air locked shut all but one rad upstairs closet the boiler or airing cupboard

Then turn the heat on doesn’t matter if the boiler doesn’t fire you will hear a load of air move and you will need to bleed the upstairs rad that’s still on

Then repeat for the rest once that ones hot
 

John.g

Messages
2,497
System or boiler HX may now be clogged with sludge after drain down but hopefully not if water was clean before draining. It may be air still trapped somewhere, if external pump fitted have you vented it by slackening the vent screw (if fitted). Also suggest turning up pump speed to max for awhile (after noting original setting).
 

Ric2013

Plumber
Messages
3,483
You say the outlet pipe gets hot. This suggests a mimimal movement of water. I'd expect the outlet to be hotter than the inlet but for the whole to get progressively warmer were it flowing properly. Almost certainly a circulation issue and I'm with Shaun on this (as usual). Airlocks are not uncommon with open-vented systems. If you can turn up the pump without contravening gas laws, then do, as John.g has suggested.

If you have a small tank in the loft for the radiators, then you very probably do not have a system boiler. As a system boiler contains the pump and an expansion vessel. Something in your description does not add up.
 

diy_massacre

Messages
38
You say the outlet pipe gets hot. This suggests a mimimal movement of water. I'd expect the outlet to be hotter than the inlet but for the whole to get progressively warmer were it flowing properly. Almost certainly a circulation issue and I'm with Shaun on this (as usual). Airlocks are not uncommon with open-vented systems. If you can turn up the pump without contravening gas laws, then do, as John.g has suggested.

If you have a small tank in the loft for the radiators, then you very probably do not have a system boiler. As a system boiler contains the pump and an expansion vessel. Something in your description does not add up.
The outlet temp of the boiler is very hot but the inlet not, but the inlet is not. Thats consistent with the boiler being turned on and off for a short while.

There is a pump in the loft so will have a go at venting it, it was already on max power.

Ii totally agree with the circulation conclusion, the water was mostly clean apart from one rad.

Thanks for the point on a system boiler I thought it was.
 

diy_massacre

Messages
38
You say the outlet pipe gets hot. This suggests a mimimal movement of water. I'd expect the outlet to be hotter than the inlet but for the whole to get progressively warmer were it flowing properly. Almost certainly a circulation issue and I'm with Shaun on this (as usual). Airlocks are not uncommon with open-vented systems. If you can turn up the pump without contravening gas laws, then do, as John.g has suggested.

If you have a small tank in the loft for the radiators, then you very probably do not have a system boiler. As a system boiler contains the pump and an expansion vessel. Something in your description does not add up.
Hi Ric,

The external pump in the loft went well and I can hear the pump working and some bubbles shooting through the pump.

Unfortunatley the boiler still closes down after 30 seconds of operation, either for hot water or central heating.

Any other ideas?

Best Matt
 

John.g

Messages
2,497
I would connect the pump to a independent power supply (extension lead), switch off the boiler and keep circulating water with continuous venting "everywhere" or/and as suggested shutting off most of the rads selectively until air expelled. What is the vent & cold feed arrangement? because (if its) the combined type are notorious for entraining air when refilling unless its done extremely slowly.
 

diy_massacre

Messages
38
I would connect the pump to a independent power supply (extension lead), switch off the boiler and keep circulating water with continuous venting "everywhere" or/and as suggested shutting off most of the rads selectively until air expelled. What is the vent & cold feed arrangement? because (if its) the combined type are notorious for entraining air when refilling unless its done extremely slowly.
Hi John,

Thankyou for responding!

When I switch the boiler on HW or CH setting the pump in the loft goes on and stays on despite the boiler shutting off after 30 seconds, so dont think I need a separate supply to keep the circulate the system going as it stays on from a separate electronic controller. Is that right?

I will try shutting off all the rads selectively, and try and track down the air pockets for each rad independently, will come back on this one...

"What is the vent & cold feed arrangement?" - If I understand you correctly the radiator cold feed arrangement comes from the small header tank and there is an overflow pipe hovering over it, I suspect this is the expansion/ aerator refill pipe not but 100% sure. The cold water for the taps is fed from a larger cold water tank.

"when refilling unless it's done extremely slowly" - I dont understand your comment isn't there only one speed to refill the system from the header tank?

Many thanks Matt
 

John.g

Messages
2,497
Pump running constantly probably OK.
Combined vent&cold feed as shown.
When refilling the system, open the (empty) header outlet valve first then tie up the ball cock to allow a trickle of water to flow, this helps to allow the air to vent and the water to flow through the same (combined) pipe. I have a isolating gate valve on my system so I can just crack it open to control the water to the ball cock.

Is there a vent plug in the centre of your circ pump?? you might post a picture of your pump showing the model details etc.
 

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diy_massacre

Messages
38
Pump running constantly probably OK.
Combined vent&cold feed as shown.
When refilling the system, open the (empty) header outlet valve first then tie up the ball cock to allow a trickle of water to flow, this helps to allow the air to vent and the water to flow through the same (combined) pipe. I have a isolating gate valve on my system so I can just crack it open to control the water to the ball cock.

Is there a vent plug in the centre of your circ pump?? you might post a picture of your pump showing the model details etc.
Hi John,

Many thanks for your reply!! First of all, attached photos one with red circle shows aerator tucked away.

Yes the pump has a drain plug, see picture and I have bleed it until water comes out. It also has a motorised switch valve to switch HW and CH. I looked up my boiler type and it has an external pump so thats the only one.

I get your slow fill solution where you tie up the ball cock to slow the water inflow, but I have a stop-cock going to the header tank so could I partially open it ( a tiny bit) to achieve the same slow rate? The tank is pretty inaccessible at the peak of the roof. I will try the slow fill idea and come back...

My boiler is on the ground floor, the pump in the attic and it switches itself off so suspect the air pocket is in the boiler loop.

Many Thanks Matt
 

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Ric2013

Plumber
Messages
3,483
Agree on using stopcock to control flow. Note that it may help to manually set the 3 port valve near the pump to the midway position for now. I suspect the problem is the pump is having to try to force air down to try to bring it back up to where it can vent to atmosphere. Pumps don't actually work well when they're up high - they need to PUSH against the water, not PULL it up. What you have is one of those badly designed systems that does this when drained. If the original installer fitted air vents, then great, but you need to find them: there's one to the left of the pump, by the way.

I'd actually be tempted to buy some new pump washers in case you need them and (with the boiler off) temporarily reverse the pump and see if that clears anything. Waiting for a gas installer to say why this might be a bad idea.

By the way, that pump will last longer is the shaft can be set to a near-horizontal position. Shouldn't be vertical!
 

John.g

Messages
2,497
I think those aerators are notorious as well for getting blocked but can't see any easy method of removing it short of cutting the pipework, if you wish to try filling the system very slowly, ensure boiler and circ pump off, shut that valve and drain down the whole system again, shut the drain valve then just crack open the valve until you get a trickle of water to the header tank. there is a manual vent on a bit of vertical piping adjacent to the pump, if you could remove this completely while filling but to avoid sitting along side it for a long time you might be able to attach a bit of tubing to it and put it in a bucket or whatever. Not familiar with that mid position motorized valve but you should be able to latch it in the mid position so that both the rads & cylinder coil are venting/filling together.

Also, after refilling, perhaps try pump on minimum speed or speed 2.

Incidentally, @Ric2013, those Selectrics seem to be indestructible as I have seen a number of them installed vertically and they are all > 15 years old. I think the above pump is week 40 2007, (PC:0740)
 
Last edited:

diy_massacre

Messages
38
Agree on using stopcock to control flow. Note that it may help to manually set the 3 port valve near the pump to the midway position for now. I suspect the problem is the pump is having to try to force air down to try to bring it back up to where it can vent to atmosphere. Pumps don't actually work well when they're up high - they need to PUSH against the water, not PULL it up. What you have is one of those badly designed systems that does this when drained. If the original installer fitted air vents, then great, but you need to find them: there's one to the left of the pump, by the way.

I'd actually be tempted to buy some new pump washers in case you need them and (with the boiler off) temporarily reverse the pump and see if that clears anything. Waiting for a gas installer to say why this might be a bad idea.

By the way, that pump will last longer is the shaft can be set to a near-horizontal position. Shouldn't be vertical!
Hi

Thanks for the response Ric

Pity its a poor design but I need to live with it at the moment. Yes I saw the vent and tried a screwdriver but it's tight, I have some WD40 on it now and will try later.

Wil also try the motorised valve at half-mast to do both heating and rads at the same time.

I like the reverse pump idea and think as long as the boiler is off is likely to clear but will try a slow-paced fill first as John suggests.

Many thanks Matt
 

diy_massacre

Messages
38
I think those aerators are notorious as well for getting blocked but can't see any easy method of removing it short of cutting the pipework, if you wish to try filling the system very slowly, ensure boiler and circ pump off, shut that valve and drain down the whole system again, shut the drain valve then just crack open the valve until you get a trickle of water to the header tank. there is a manual vent on a bit of vertical piping adjacent to the pump, if you could remove this completely while filling but to avoid sitting along side it for a long time you might be able to attach a bit of tubing to it and put it in a bucket or whatever. Not familiar with that mid position motorized valve but you should be able to latch it in the mid position so that both the rads & cylinder coil are venting/filling together.

Also, after refilling, perhaps try pump on minimum speed or speed 2.

Incidentally, @Ric2013, those Selectrics seem to be indestructible as I have seen a number of them installed vertically and they are all > 15 years old. I think the above pump is week 40 2007, (PC:0740)
Hi John

Thank you for your extensive input, much appreciated!!

I would rather not cut the aerator out just yet, also in an awkward place.

I will try the slow fill process and I like your idea of having a pipe on the open aerator manual screw, it currently has wd40 on it as it's stuck fast.

Can put the pump at 2 if that helps. I assume it was put at 3 due to the 8mm rad pipes.

Will come back later with the results.......

Many thanks Matt
 

John.g

Messages
2,497
Judicial (whatever that means) application of a vise grips should shift that without kinking the pipe!.
 

diy_massacre

Messages
38
Judicial (whatever that means) application of a vise grips should shift that without kinking the pipe!.
Thankyou John, it's been wd40'ed so should be better than before!

Right, I am on my way to try but just thought I would share with you the rad heating circuit piping pictures, maybe you might be able to cast some light onto this standard as I have never seen it before?

Thats 22mm to multi 8mm connectors, or alien invasion....

Many thanks Matt
 

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diy_massacre

Messages
38
No Matt,
Havn't seen/heard of that before.
Hi John and earlier Ric,

Thank you for your advice, I drained the boiler component of the system this evening and slow filled the system and with a bit of gurgling its working on most of the radiators in the house which is great news. I found 5/additional bleed points ( some clagged up ) in the loft and suspect that will resolve the additional radiators and indirect tank.

My new rad and the solder joints held so all positive there too!

A BIG THANKYOU FOR ALL YOUR KNOWLEDGE, HELP AND IDEAS !! I wouldn't have solved it without you.

The very best to you both

Matt
 

Reply to After new rad fitted boiler doesn't want to switch on in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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