Gas boiler doesn't push hot water to CH and Bath

[Mountain]

We have combicompact vcw gb 221h vaillant gas boiler pump type: vp5-ze 15, which has gone faulty. The picture of main parts can be seen here: http://2move.me.uk/boiler.jpg . It has suffered from the same fault for years but has not been difficult to remedy within a few hours or a day or two. But this time the fault refused to go away like before. The fault is this: When the fault starts, the boiler doesn’t push hot water into central heating and bath hot water tank. The water at sink tap becomes extremely hot, almost to the boiling point. The boiler externally becomes hot a lot more than usual.

Before whenever the fault started, I put the main electricity and pilot light off and opened hot water tap at the sink to let all hot water comes out. After that I left it for a few hours until it became cold completely. When it became cold enough I put main electricity switch and pilot light on. Most of the time it restarted working all right on the first attempt. Some times I had to repeat the operation a few times until it worked. This some times took a day or more. But when it worked, it continued working for a few months before the fault came back.

Recently the fault started to come back early almost within a week. Finally the fault refused to go away any more since over a week ago. I gave up and decided to call a plumber to check it. We suspected some thing was wrong with pump but the pump was working. Everything else was in order. Finally we decided the cause must have some thing to do with the pump. So we decided to change the pump. The plumber closed central heating and hot bath water switch off but left sink hot water tab switch on. Today I was planning to go out to shop for the pump. But before I went out for curiosity reasons I put central heating and hot bath water tank switch on. It immediately started working. Now I changed my mind to buy a pump before I find out more.

Now please is this fault has some thing to do with the pump or something else? Please help. It will come back soon and it is very cold.

 

[buck51]

When the fault is pressent is there power to the pump? If yes, then is the pump running or is it jammed ?

 

[Fluffster]

Your secondary hot water heat exchanger is knackered (the black plastic unit on the left of the boiler) these are common failures and have been replaced with a stainless steel unit.
Also I take it you re pressurised the circuit up to 1 bar as the reading is zero in the pic.

Pete

 

[Mountain]

Your secondary hot water heat exchanger is knackered (the black plastic unit on the left of the boiler) these are common failures and have been replaced with a stainless steel unit.
Also I take it you re pressurised the circuit up to 1 bar as the reading is zero in the pic.

Pete

This is because it was leaking a bit and was like that for years . But last year we closed the point of the leak. What you see are sedimnets left because of the viporization of leaking water. The plumber increased the pressure to 1.50 bar. But that didn't help as the plumber expected. The following day, unexpectedly started working when I gave it a try for the last time before going out to shop for the pump.

Regards

 

[DP]

If the pump did NOT work properly, boiler would not EVEN start.

Hot water can come out very hot out of this boiler, so switching off and running a hot tap to cool the water is no remedy- all you are doing is removing heat from the HW heat exchanger. Boiler does not have any tanks or containers that hold hot water. Boiler heats water when you need hot water.

Get someone who knows this boiler instead of changing parts without proper thought. To not follow advise will be an expensive exercise.

 

[Mountain]

When the fault is pressent is there power to the pump? If yes, then is the pump running or is it jammed ?

Yes certainly. The plumber thought the pump was working by listening to it with a long metal between the pump and his ear. He checked every thing and thought each one was in order. He puzzled as why the hot water not going to the C. H. and bath hot water tank. Later he removed the big srew on the centre of the pump. After that he said the pump was faulty and has to be changed.

Regards

 

[Mountain]

If the pump did NOT work properly, boiler would not EVEN start.

Hot water can come out very hot out of this boiler, so switching off and running a hot tap to cool the water is no remedy- all you are doing is removing heat from the HW heat exchanger. Boiler does not have any tanks or containers that hold hot water. Boiler heats water when you need hot water.

Get someone who knows this boiler instead of changing parts without proper thought. To not follow advise will be an expensive exercise.

I understand that. Nevertheless, in addition to other tricks, that was one of the tricks, made it to work. Finally, none of the tricks could make it to work. When the fault comes back again I will cut the power from the pump to see what happens.

Regards

 

[Mountain]

I have discovered what is wrong with my boiler. It is the pump which is faulty. Some times stucks. I remember once the starter of my van was not working. So the AA man knocked it with a hummer. It worked. I did the same thing with the pump of my boiler. It started working immediately after a few light knocks with a hummer.