I have an open vented gravity fed system operated by a baxi bermuda 401 back boiler and trv's on all rads except one. About a week ago I bled a couple of rads but with the central heating on . That evening I came home to check if rads were ok and found that none were working. My initial thoughts were that I had an airlock in the system. I have now bled all rads and also the pump, although no air or water was released from the pump. The spindle inside the pump was spinning fast and quietly. The F&E tank in the loft has water in it and appears ok. I have an old ACL Lifestyle midpoint motorised valve on the system and neither the manual valve on the side or the lever for W M H can be moved at all. I am a total novice and have only checked these things from looking for advise on the web. The lever on side of motorised valve is stuck on H and will not budge, also the manual lever is impossible to move. Before I go and purchase a replacement valve are there any other checks I can carry out to see if the fault lies elsewhere, although from what I have read I think the mid point valve will need replacing regardless. Thanks.