Boiler only coming on for a minute, system problem?

Hi guys, i am new to this forum and appreciate any help that can be offered as i'm really at my wits end with my central heating system. I have had a friend who is a plumber to trade look at and he has drawn a blank also!!

Open vented system with header tank in the attic

Potteron Suprima 80L boiler - PCB and stat have been swapped out last month but to no avail

8 K2 rads and one towel rail (upstairs bathroom), all rads have TRV's and were fitted along with new pipe work (Hep 10mm) 2 months ago.

New pump fitted last month, again no avail. System has been drained, de-sludger placed in system, drained again with inhibitor placed in system upon refill.

The problem i have seems to be that the heat is getting away from the boiler. When the boiler inititally fires up it stays on for around about 8 mins, then overheats. After this the boiler will come on for a minute or so then cut out for 2, back on for 1 and off for 2. It carry's on like for the rest of the time it is on.

The stat in the hall is set to 21 degrees, and i can safely say that this temp is never reached. The rads get warm but are by no means burning. Due to this it takes an age for any kind of heat to build up the house.

What i have noticed is that the flow coming out of the boiler is really hot, so hot you couldn't keep your hand on it, but the same flow pipe that goes into the pump under my stairs is luke warm at best just before it goes into the pump. The distance from the boiler to the pump is about 3 metres.

I disconnected the flow pipe from the boiler and from teh pump and blew through it, there didn't appear to be any blockages, i did the same with the return with the same results. Unfortunately i can't see the pipe from the boiler to the pump as it goes under a tiled floor.

I also noticed that the first rad (600 K2 in the hall) and the towel raile (highest point) need bled once a week at least. Not sure if that has any bearing.

Any suggestions as to what could be the issue here?
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Sorry, i meant heat is NOT getting away from the boiler

Hot water ok?

Diverter or Zone valves?

By-pass arrangements?

Pump valves open?

filter on the flow before the pump??? big brass thing with an handle??

could be:

piping wrong

dodgy bypass

still blockage

balancing way off

pump valves not fully open

gate valve on main flow or return not fully open

pump not working to spec

Thanks guys

Answers in line, or as best i can anyway!

piping wrong - Which piping are you referring to, the new Hep which i ran?

dodgy bypass - I suspected the towel rail up the stairs was acting as a bypass as it is the only radiator that was really burning. I shut this off at the locksheild and the TRV but to no avail.

still blockage - Not sure what this means?

balancing way off - Can you explain why this would affect the system? Excuse my ignorance. All the rads seem to burn about the same

pump valves not fully open - My plumber friend checked this

gate valve on main flow or return not fully open - I'm not sure if there is a gate valve, how do i find out?

pump not working to spec - 2 pumps now so i suspect this isn't the case

filter on the flow before the pump??? big brass thing with an handle?? _ Can't see any filter

Hot water ok? - Hot water is working fine, no issue's there. Issue with heating happens when hot water is on and off

Diverter or Zone valves? There are 2 zone valves under the stairs after the pump

Hope this helps guys. Just got a gas bill through and its sky high, i assume the boiler going on and off like this is very wastefull?

furrock said:

Thanks guys

Answers in line, or as best i can anyway!

piping wrong - Which piping are you referring to, the new Hep which i ran?

dodgy bypass - I suspected the towel rail up the stairs was acting as a bypass as it is the only radiator that was really burning. I shut this off at the locksheild and the TRV but to no avail.

still blockage - Not sure what this means?

balancing way off - Can you explain why this would affect the system? Excuse my ignorance. All the rads seem to burn about the same

pump valves not fully open - My plumber friend checked this

gate valve on main flow or return not fully open - I'm not sure if there is a gate valve, how do i find out?

pump not working to spec - 2 pumps now so i suspect this isn't the case

filter on the flow before the pump??? big brass thing with an handle?? _ Can't see any filter

Hot water ok? - Hot water is working fine, no issue's there. Issue with heating happens when hot water is on and off

Diverter or Zone valves? There are 2 zone valves under the stairs after the pump

Hope this helps guys. Just got a gas bill through and its sky high, i assume the boiler going on and off like this is very wastefull?

Click to expand...

any part of the piping could be wrong

follow the main flow pipe and the main return and see if there is a valve on somewhere

dodgy bypass as in: a direct connection between flow and return, with or without a valve in it.

blockage as in blockage: lump of shyte in the main flow or return that restricts the flow; x400 does not remove all carp

if your lockshields are too closed, especially if there IS a bypass, the water will go directly back to the boiler leaving your rads pi55warm and causes your boiler to cycle. and i don't mean on a bike.

furrock said:

Hot water is working fine, no issue's there. Issue with heating happens when hot water is on and off

Click to expand...

Interesting.

With hot water and central heating running measure the return temp and the flow temp at the boiler. Turn off hot water and measure the temperatures again.
What pump is fitted and what setting is it on?

Answers:

follow the main flow pipe and the main return and see if there is a valve on somewhere - Like i i say the only length of pipe that i can't see if the tw directly from the boiler to the oump and back. The lengrtth of this pipe must be 3meters. Is it normal that the flow is burning hot at the boiler and yet 3m away it is luke warm?

blockage as in blockage: lump of shyte in the main flow or return that restricts the flow; x400 does not remove all carp - We did disconnect the pipes and blow down them, all seems ok.

if your lockshields are too closed, especially if there IS a bypass, the water will go directly back to the boiler leaving your rads pi55warm and causes your boiler to cycle. and i don't mean on a bike. - Is it worth while me opening up all the locksheilds and TRV's to see if this helps? The locksheilds need 5 revoloutions to be fully opened

With hot water and central heating running measure the return temp and the flow temp at the boiler. Turn off hot water and measure the temperatures again - What tools do i need to do this?


What pump is fitted and what setting is it on - British gas Grundfos, set to 3

Thanks guys

As your hot water is OK this is a not so probable cause but have you checked that the ball-cock valve in the Fill & Expansion tank is working and that there is some water in the tank?
If there is no significant hot water flowing, then the pipe near the boiler will get warm, due to heat conduction from the boiler and further away it will be cool /cold.
Are the zone valves working? It is unlikely that they will both fail at the same time but can you hear / see them change over when the heating is selected on? (get your mate to help.) If neither is working then have you got a problem with the electrical supply from the programmer to the valve motors?
Can you hear / feel the circulating pump running? (Try a screwdriver with the tip touching the motor case and your ear to the handle end.) If not, close the two isolating valves either side of the pump, take out the big bleed screw, switch on for a few seconds and see if the pump turns. If it doesn't, try turning the centre with a quick twist with a screwdriver. Don't forget to put the bleed screw back before you open the isolating valves. Then loosen the screw slightly for a few seconds to bleed any air out of the pump.)
Other than that, it does sound like a blockage somewhere.

Zone valves seem to be working fine. When i turn the room stat down to when it clicks (normally about 18 degrees) i can hear the zone valve make a noise.

All seems to be fine with the pump, i can hear it whirring away no probs.

The flow pipe does get warm before it goes into the pump after a while, but it does take a while and it doesn't get as hot as the flow right next to the boiler.

I traced the towel rad pipe out and it is T'd in after the pump, and in between the zone valves. Whats weird is the return from the towle rad seems to some how tie back into the flow that goes up to it. This may just be my interpretation of it though, but thats how it looks. A note above says that shutting the towel rail off at the locksheild and TRV could be a bad idea. Is there any other way i can take this out the equation, if its worth it of course? As i said before the towel rail is the only radiator that truly burns.

All the pipe work is new apart from that one length under the floor into the boiler. So if there is block it has to be there, but surely by being able to blow through both pipes with ease this proves no block?

I forgot to mention that this problem was happening before i change the rads and pipework out.

Does anyone have anymore thoughts on this?

furrock said:

Does anyone have anymore thoughts on this?

Click to expand...

Yes, if hot water is running off the boiler ok.

You have got your heating pipes crossed/blocked or incorrectlly installed.

Which pcb did you replace it with... part No