What is this and can you help?

[mk2phil]

Hi there,

Last week the central heating system starting making a loud screeching and banging noise. We traced it to the GRUNDFOS pump which we removed and replaced yesterday. After we re-opened the isolating valves on either side of the pump, we bled the pump and started the central heating system.

After about 15 seconds the pump started scavenging and getting louder. We opened one of the bleed valves on a radiator and no air or water came out – it was empty. Tried all the rads on the first floor and they were all empty.

Then we checked the HW tank and found that the motorised valve on the HW side of the system wasn’t opening (I think it’s an ‘S’ plan; we have 2 motorised valves) – after removing the motorised head you could hear the motor trying to work. We manually opened the valve and tried the HW again.

After about 10-15 seconds the same thing happened; the pump got louder and we heard hot water coming out of the expansion pipe over the header tank in the loft. We tried to drain the system thinking it might be an air lock, but when we got the boiler (an old BAXI type) we couldn’t find a drain cock. However we did find a large cube type thing on the inlet side of the boiler with a fitting underneath. Does anyonme know what this is? We didn’t want to start trying to open it in case it broke – the boiler is about 30 years old. My dad thinks there might be a filter in there or some kind of valve that could be stopping the water from filling the system? Anyone know what it is?

Then we tried draining the system from one of the rads downstairs – a bit of water came out but not much. Went and checked the header tank in the loft and it was still completely full.

There’s nothing in the header tank causing a blockage.

My suggestion is that the motorised valve has failed causing the boiler to spit water out into the expansion tank. Because the system isn’t filling properly, this has run the pump dry and knackered it. Don’t know why the system isn’t filling back up though?

Can anyone suggest what we should try next or why the system might not be filling..?

Thanks in advance, Phil

 

[scatmanjohn]

The cold feed is blocked.

Also the fact that you have got your boiler in bits is a major concern.

I'd suggest you employ the services of an expert before doing anything else.

 

[wiggikins]

Ditto!

 

[baxpoti]

However we did find a large cube type thing on the inlet side of the boiler with a fitting underneath. Does anyonme know what this is?

This is the injector tee and should have been removed when the boiler was modified to fully pumped.

Messing about with this type of gas appliance can seriously damage your health (let alone killing your family).

 

[Agile]

Did you remove the front cover from your boiler or was it just missing?

Presumably there is/was a fire at the front?

Removing the firefront should only be done by somebody who is competent to work on gas, that means CORGI registered.

Since your problem is just a blocked feed pipe then its nothing to do with the boiler.

Tony

 

[twgas]

This is the injector tee

agreed

should have been removed when the boiler was modified to fully pumped

not so sure, thought this spreaded the water coming back to boiler under pump pressure. I apologise in advance if I'm wrong.

OP still needs an expert in to re-assemble and test boiler.

 

[baxpoti]

No appology required this is correct for the 551

 

[LUNAT]

HI

sorry not trying to be rude but the OVERFLOW pipe you mentioned is not overflow. .
if you do not know the boiler why remove gas fire,front cover,etc,

 

[twgas]

Apology accepted

just checked MI on parts arena, found this;

i) THE INJECTOR TEE MUST BE FITTED TO THE BOILER RETURN CONNECTION ON ALL SYSTEMS

 

[londonboy123]

my nan has a back boiler (gas) and a fully pumped system (3 port mid, grundfos 15:50 pump, etc) - i thought injector tees were only used on gravity h/w and pumped heating systems?

 

[namsag]

Think about it although baxi casting comes in 2 halves each half has 4 waterways going across it. If it did not have the plastic spreader bit fitted into bottom connection (they didn`t all have the metal T block) the return water would shoot straight through the adjacent waterway thus causing uneven heating.

 

[DP]

Heat exchanger on 551 needs cleaning.

 

[twgas]

No appology required this is correct for the 551

thanks bp, keeps me on my toes and I did have to double check

 

[baxpoti]

i thought injector tees were only used on gravity h/w and pumped heating systems?

Not on the 551

 

[mk2phil]

thanks for the reply guys.

With regards to the boiler, we just removed the front face plate. We were hoping there was a Drain Cock near it somewhere but alas there wasn't.

The injector tee that you've identified - do you think this could be the cause of the blocked feed? Or is it more likely to be in the pipework from the header tank to the boiler?

Thanks again