Draining an unvented system and blockage in system

[bellap]

I have an Amptec electric central heating boiler that serves my radiators only. My hot water system is separate and comes from an unvented tank.
I assume that the Amptec boiler is classified as an unvented system.
I had my radiators replaced and one removed. The system was drained from a draining point. Now it's refilled there is clearly a blockage as the water won't pump around the radiators. The hot water seems to be travelling in a loop from the boiler through the pump ie only going into the pipework a foot away from the boiler. The pump gets very hot.
I've bled the radiators, bled the pump and bled the vent at the highest point of the system. I've had two plumbers out on very expensive call out charges: the first said it was a blockage in the pump but it was too hot for him to bleed (so I did it, there was little air in it). The second said the system needed a power flush but was here for 10 minutes and didn't re-drain the system or look at the pump. What can I do myself? Do I re-drain the system and see what happens when I re-fill it? When the radiators were fitted the plumber did not flush the system through afterwards.
Hope someone can help me as I can't afford the £400 for the powerflush, and what happens if that's not the problem.

 

[Softus]

Is there an isolating valve on each side of the pump?

If so, are they both open?

 

[Slugbabydotcom]

Pump could be stuck or someone has opened the bypass too far.

 

[Agile]

As its very hot it sounds as if the pump is not rotating.

Shouldn't whoever replaced the radiator be sorting out the problem?

Tony

 

[simond]

Clearly whoever replaced the rads caused the problem, or are we reading that into your interpretation? Sometimes customers tell you everything but the pertinent facts.......

How long ago were the radiators replaced and did you do it, or a tradesman? The fact that you said the system was drained from a draining point is interesting as I do not see why this would be of any interest to a householder.

Why did you have the rads replaced, were the reasons technical or aesthetic?

And where did you find an emergency call out plumber who said the pump was too hot to bleed. That is the most incredible thing of all.

 

[bellap]

There are isolating valves on each side of the pump - these haven't been touched by anyone so I am assuming they are open but will check.
The radiators were replaced for aesthetic reasons although only one had been working last winter (I have four) and I thought it was the valves. The radiators were replaced by someone who was doing some work in my kitchen so he wasn't a trained plumber, one of those I-do-everything guys. He replaced a small piece of copper pipe as well and replaced it with chrome.
The plumber who said the valve was too hot (it was very, very hot) was from Fix-It dot com but I think they sub-contract (someone from The Academy came). The second plumber was recommended by Amptec so I'll be letting them know what happened.
Shall I look at the pump then? bp

 

[bellap]

How do I check the bypass to the pump? But again, nothing has been touched by anyone other than at the bleeding point.

 

[gas4you]

Undo the large screw in the middle of the pump and remove. Insert a flat bladed screwdriver into the hole and locate on the spindle. See if you can turn the spindle, if not keep trying as sometimes they can stick quite bad.

Put a towel under the pump first as you will lose a little water from it.

 

[bellap]

Thanks Dave. I'll try that now.

 

[bellap]

Dave, I've tried to move the spindle but I can't. It is difficult to get access to the pump without loosening the nuts holding it in place (so that I can swivel it around) and my spanner isn't big enough.
I'll have another go tomorrow.
I've also drained the system and alot of air appeared to come out.
bp

 

[Slugbabydotcom]

How do I check the bypass to the pump? But again, nothing has been touched by anyone other than at the bleeding point.

Based on my first interpretation of an earlier quote :-

The hot water seems to be travelling in a loop from the boiler through the pump ie only going into the pipework a foot away from the boiler.

I figured it was possible that there was a bypass and the water was short circuiting through it.
A by-pass is just that! A short circuit usually with a valve in it to reduce the flow, however if too much water goes through by a valve being opened fully then the water will take the easiest route through this valve instead of going through your rads.

The purpose of a bypass if fitted is to protect the pump should all TRV's become closed.
Some boilers must have a set temperature difference between flow and return and a bypass is a method of achieving this.

It is something I have come across when 'General doers of things' start playing with heating systems they dont understand.