Glow Worm Inset BBU40. No heating or hot water

[Mick10256]

Hi all,

Called to give a second opinion on this. Conventional open vented system. 22mm feed to 3 port valve 22mm primary feed to cylinder with a 15mm return to common 22mm return. When demand for hot water only, the primary feed pipe to the cylinder heats up within a few seconds to the full boiler temp of 70 degrees but the return pipe stays cold and the DHW is barely warm after an hour. The heating is in 8mm micro bore and over the last year has gradually stopped working. I managed to get two upstairs rads working by shutting off all down stairs. My first thought was the pump, which was replaced only two years ago. I replaced the pump with a new Grundfos 6 meter one with no effect. The system was power flushed and a spirotech fitted three years ago and customer said it worked for about a year after that.

Any clues on this one would be much appreciated. Has anyone come across heat exchanger problems on the inset BBU 40 that would give these symptoms?

Thanks in advance,
Mick

 

[lame plumber]

are you in a hard water area, then a build up of calcified crud would be my opinion, otherwise old boiler and micro bore would also indicate sludge issues, after all nice new circulators dont like crud at the best of times and can slow down quickly in dirty conditions. Did the powerflush actually clear out all the sediment, a quick flush could have caused more issues rather than reducing problems, the state of the spirotech contents would indicate the state of the system

 

[SafeGasInstall]

did you break into the pipe work to look for blockages , did you look in the f&e ? did you have the 3 port a part to make sure is functioning ok ? also did anyone do anything to the system to eliminate air lock ? had a air lock once on a micro bore open vent it took me 6h and then I gave up and went home about 1am , next morning I got there 8am and it was running ok

 

[RoryD]

I'd undo the return and draw water off until hot. I would also check if there is a blockage at the cf joins the system. If that's on the return it will be incorrectly configured but my bet is if it is, it will be blocked.

 

[SafeGasInstall]

not been silly but you have checked the ch filter valves

 

[Mick10256]

Thanks guys. Lots of questions.
Spiro is clean, fe is clean and full, when I took old pump out it was clean, all rads bleed clean water, cf is in the correct place on the feed pipe, dissolved solids around 380ppm, but I've ripped out boilers from this area and none showed scaling. Haven’t disconnected any pipework yet but I think I’ll concentrate on the lack of flow affecting the DHW. Can’t get my head round the fact that the primary feed to the cylinder gets hot quickly when the valve calls for heat (indicating a reasonable flow?) but the DHW is cold. Just like when the static head of the pump pushes against an air lock but no water is actually flowing. Now been on hot water only, no heating, for 8 hours and still cold! Yep I’ve had air locks from hell too.
BG told cust they needed new boiler, HE blocked, that’s why they asked for a second opinion and when I saw 8mm micro bore I told them to hang on a bit. In my short 10 years I've never had an old cast iron HE get blocked.

 

[SafeGasInstall]

I would fit a drain of on the return and run boiler and open drain of to run some water to eliminate air lock in cylinder and blockage to the return ,
is there a return valve to boiler ? i would not trust BG .....they might have cause this by turning it off , i know it sound silly but i am sure you have eliminated that

 

[tamz]

It won't be the heat exchanger on a back boiler. A half brick wouldn't block that. Time to start cutting or disconnecting pipes starting with the return from the coil.
Sometimes you are quicker and easier repiping than pyssing around.

 

[Mick10256]

Thanks SafeGas,

will be cutting into the system next week as booked solid. Thought the summer use to be slow but still getting no heat calls! Will cut into the return and see what condition is like. Feed seems to be fine. Hate laminate flooring, all through the house. Big job me thinks.

 

[Mick10256]

Yes Tamz, my thoughts exactly. I've never seen one. Has anyone seen a cast iron HE blocked solid?

 

[tamz]

Never.
You wouldn't block it if you filled it with cement slurry :smile:

 

[Reg Man]

Still sounds like a pump or zone valve issue. Can see why 8mm would be prone to blockage but not the indirect HW vessel coil. Depending on how high up the system the cold feed tee's in, it might be worth checking if the cold feed is blocked.